The specific claim that they didn't eat meat before age 10 is not something I've ever heard before and the author in question does not cite any sources I can use to evaluate it. My instinct would be to say this is not true, since it is an extremely blanket statement that I think would be difficult to prove conclusively for all time periods of the cultures listed. Evaluating meat consumption in young children is made more difficult by the fact that stable isotope analysis used to determine meat consumption (δ15 N) is also affected by breastfeeding (you know, since milk is an animal product), so it would be hard to distinguish archaeologically between a child who has concentrations of this isotope in their bones from breast milk in infancy and one who gets it from meat. Maybe by 10 years old it would be more obvious but at very young ages this would be difficult to assess.

The more interesting way to ask this question would be to ask "Were Mesoamerican diets largely vegetarian?" The answer to that is... yes and no... Commoners ate largely vegetarian diets in many parts of Mesoamerica. Mesoamericans had a process of treating corn with lime (as in, the chemical lime not the fruit) called "Nixtamalization" which experimentation has shown chemically altered the maize to increase its protein content (Sefa-Dedeh et al. 2004). When eaten in conjunction with beans, this could theoretically provide all the essential amino acids the human body needs. This means that the Mesoamerican Trinity of crops, maize, beans, and squash, is a complete diet at least as far as most macro-nutrients go. Of course, the fact that the Mesoamerican diet didn't require meat doesn't mean people didn't eat it.

First, Mesoamericans had access to domesticated turkeys and dogs (both of which were eaten) as well as wild game (birds, deer, waterfowl, iguanas, etc.) and fish. There is ample archaeological evidence of the consumption of all of these among all three cultures you listed including faunal remains in archaeological sites with indications of human consumption (Götz and Emery 2013).

Isotopic studies of human remains recovered from archaeological sites can reveal, indirectly, the relative meat consumption of a given group as measured in δ15 N concentration. There are other factors which can affect δ15 N so this only really serves as an effective relative measure. Studies of this variety have shown that, by and large, Mesoamerican meat consumption was relatively low and consistently so despite changes in relative importance of different plants over time (White and Schwarcz 1989). There are some indications that meat consumption was higher among elites than commoners (Chase et al 2001), but the clearest trend relates to those communities near the coastline which had regular access to fish (Wright 2004). Fishing formed a major part of the economy for many Mesoamerican societies, especially those located along coasts or lakeshores. Early Mesoamerican cultures, like the Olmec, relied very heavily on fishing and other aquatic resources.

So, the short answer to your question is that it is not accurate to say their diets were 100% vegetarian, however their levels of meat consumption were substantially lower than ours and many other cultures throughout history. Additionally, their diet of (chemically treated) maize, beans, and squash was capable of providing for their nutritional needs without meat.

Sources:

• Chase, A.F., Chase, D.Z., White, C.D., 2001. El paisaje urbano Maya: La integración delos espacios construidos y la estructura social en Caracol, Belice. In: Ciudad Ruiz,A., Iglesias Ponce de Leon, M.J., Martínez Martínez, M.d.C. (Eds.), Reconstruyendo la Ciudad Maya: El Urbanismo en las Sociedades Antiguas. Sociedad Española de Estudios Mayas, Madrid, pp. 95–122

• Götz, Christopher M. and Kitty F. Emery. (Editors). 2013. The Archaeology of Mesoamerican Animals. Lockwood Press, Atlanta.

• Sefa-Dedeh, Samuel; Beatrice Cornelius, Esther Sakyi-Dawson, Emmanuel Ohene Afoakwa. 2004. Effect of nixtamalization on the chemical and functional properties of maize. Food Chemistry 86.3. pp.317-324

• White, Christine D., and Henry P.Schwarcz. 1989. Ancient Maya diet: as inferred from isotopic and elemental analysis of human bone. Journal of Archaeological Science 16 (5). pp. 451-474.

• Wright, L.E., 2004. Osteological investigations of ancient Maya lives. In: Golden, C.,Borgsted, G. (Eds.), Continuities and Change in Maya Archaeology. Routledge Press, New York, pp. 201–215.

Ok, so to begin with, the author does start off with a relatively sound thesis. Most Native American cultures were indeed agriculturalists who subsisted primarily on vegetables and fruits. However, she does run into several problems with the detail. Take her statement about Mesoamerican children not eating meat. The truth is, we cannot really know this. The only solid information on child diets in Central Mexico that I know of comes from the Codex Mendoza, which shows the quantity of food children ate while growing up. Even then, it was probably not a literal ration; instead just showing the relative amounts they ate at different ages. I don't remember it specifying the type of food provided, and even though maize would certainly form the bulk, we cannot say with confidence that there was no meat.

She also comments that Mesoamericans lived twice as long as Europeans (or at least that the Spanish thought so!). I'm not exactly sure where this reference came from, but it is not exactly correct anyway. According to Carlos Viesca Treviño Aztecs had an average lifespan of somewhere between 34 and 40 years (37 average), which was good for its time and better than the European average (somewhere around 25). But it is not exactly double. Furthermore, the article implies that this difference is due solely to diet, and while Mesoamerican diets were healthy, the Aztecs also benefited from good public health, effective medicine, and a lack of crowd diseases common to Europe at the time.

Later on when discussing buffalo she claims that Plains Indians did not think that the buffalo could go extinct. I'm not sure about this though. I've read a few things in passing that implied that the Plains people did recognise the impending destruction of the buffalo and understood the magnitude of the threat. But I don't know enough about this area to fact check that exact point.

Later again, she comments that meat was not considered highly among Indigenous cultures. I'm not sure about northern nations, but Mesoamerican nations definitely enjoyed and valued meat, even if they didn't eat it all that often. They domesticated and consumed ducks, rabbits, hares, turkeys, dogs, and some insects. They also ate plenty of other animals, including deer, fish, crayfish, and so on. Furthermore, they also sacrificed animals in religious rites, and sometimes animal parts were used in healing, or even in magic.

I think that the author, although making a good point about vegetables and grains in pre-Columbian diets, overstates the case. They took advantage of meat sources whenever it was convenient to do so. Native Americans certainly based their cuisine on vegetables, but they were definitely not vegetarians by ethos. Lastly, I am somewhat troubled by the last section which seems to imply that the social problems faced by Plains People is somehow due to them eating meat, rather than vegetables. Perhaps this was not intended by the author, but it came off that way to me. In any case, the problems faced on Western US reservations are complex and multi-causal, and blaming them on diet would require a very large amount of evidence, which the article does not provide.

Sources: Viesca Treviño, Carlos: - Medicina Prehispánica de México: El conocimiento médico de los Nahuas

Ortiz de Montellano, Bernard R.: - Aztec Medicine, Health, and Nutrition

Mann, Charles C.: - 1491: New Revelations of the Americas before Columbus

Berdan, Frances F. and Anawalt, Patricia Rieff: - The Codex Mendoza Volume 1-4

The author bio hints at what I think she's trying to get at here, and I do think that she's being overly broad to make a point.

Her Choctaw name, Hina Hanta, means Bright Path of Peace, which is what she considers vegetariansim to be. She has been vegetarian for over 14 years.

Unfortunately, the article does lean into a common trope of writing about Native Americans in general: the idea of a people perfectly in tune with the land and "Mother Earth," until Europeans showed up. There's certainly a lot of evidence that European settlers drastically impacted the traditional ways of life of the native people. But she doesn't show much evidence in the piece that this included a shift away from traditional vegetarian practices and towards meat.

The most indefensible line in the whole article may be this one, which is also the heart of her argument:

The trend that moved some North American Indian tribes away from plant food-based diets can be traced to Coronado, a sixteenth century Spanish explorer. Prior to his time, hunting was a hobby among most Indians, not a vocation. The Apaches were one of the few tribes who relied heavily on animal killing for survival.

What it means to rely "heavily" on something is obviously up for debate, but we have ample evidence that many Native American cultures incorporated animal killing as a integral part of their food practice. Not being an expert on Native American history at all, I'm going to focus on the one area I know pretty well, my home area of New England.

The earliest account we have of Native Americans in New England is the account of Giovanni da Verrazzano, who visited what is now Rhode Island in 1524. He describes the native population with a fair bit of detail, and notes multiple times that they hunted game as part of their diet. He was also amazed both at the fertility of the land that he visited and at the complexity and sophistication of the agricultural techniques used by the farmers.

We frequently went five to six leagues into the interior, and found it as pleasant as I can possibly describe, and suitable for every kind of cultivation-grain, wine, or oil. For there the fields extend for 25 to 30 leagues; they are open and free of any obstacles or trees, and so fertile that any kind of seed would produce excellent crops. Then we entered the forests, which could be penetrated even by a large army; the trees there are oaks, cypresses, and others unknown in our Europe. We found Lucullian apples, plums, and filberts, and many kinds of fruit different from ours. There is an enormous number of animals-stags, deer, lynx, and other species; these people, like the others, capture them with snares and bows, which are their principal weapons.

...

They live on the same food as the other people-pulse (which they produce with more systematic cultivation than the other tribes, and when sowing they observe the influence of the moon, the rising of the Pleiades, and many other customs derived from the ancients), and otherwise on game and fish.

So, yes, there was a fairly complex agricultural system in place, focused around the usual plants. But there was also plenty of hunting and fishing. This is borne out by archaeological evidence, including middens found along the New England coastline. These are piles of discarded shellfish shells, and their abundance shows a systematic exploitation of that abundant resource for food.

One thing to keep in mind as well is that corn is hard or impossible to grow in many areas of North America, including northern New England. This meant that the people of Northern Maine, for example, relied more heavily on moose and other game than their counterparts to the south. William Cronon speaks about this in his book Changes in the Land:

Grain made up perhaps one-half to two-thirds of the southern New England diet, thereby reducing southern reliance on other foodstuffs; in comparison, northern Indians who raised no grain at all had to obtain two to three times more food energy from hunting and fishing.

Notice that Cronon is saying that both northern and southern societies did rely on hunting and fishing, the only question is how much. One thing to keep in mind is that the increased reliance on hunting and fishing also had an impact on their ability to sustain a large population, as Cronon notes:

The nonagricultural Indians of Maine sustained population densities, on average, of perhaps 41 persons per hundred square miles. The crop-raising Indians of southern New England, on the other hand, probably maintained 287 persons on an identical amount of land, a sevenfold difference.

You can see the benefits of agriculture! This lends some amount of credence to Laws' overall point, that plant-based food was much more important to most native diets than we popularly think. However, it goes against her overall gist that hunting and fishing were not relied upon as part of the diet.

There's one more thing that is particularly ironic in her article, this little bit about Squanto:

Many history textbooks tell the story of Squanto, a Pawtuxent Indian who lived in the early 1600's. Squanto is famous for having saved the Pilgrims from starvation. He showed them how to gather wilderness foods and how to plant corn.

If she's arguing that Native Americans didn't kill animals, Squanto is the wrong guy to bring up! What, pray tell, was the way that Squanto told them how to plant corn? William Bradford, one of the English settlers at Plymouth, says

Afterwards they (as many as were able) began to plant their corn, in which service Squanto stood them in great stead, showing them both they manner how to set it, and after how to dress and tend it. Also he told them except they got fish and set with it (in these old grounds).

In other words, Squanto put fish in with the corn as fertilizer! There has been some questioning as to whether this was a widespread Native American practice, or not. One anthropologist/historian, Lynn Ceci, even suggested that Squanto may have learned this practice from his time in captivity in England. However, this practice has been substantiated by the discovery of fish remains in fields previously used by natives to grow corn, such as Sandy Point in Cape Cod. So, even if they were reliant primarily on corn, they killed animals to grow it.

Laws falls victim to one of the classic blunders, the most famous of which is "never get involved in a land war in Asia," but only slightly less well known is this: don't overgeneralize your findings! She may have a point when it comes to Choctaw practices, or even with Mesoamerican practices (although u/ucumu has a great post as to why she probably doesn't). She doesn't have nearly enough evidence to extend this to Native Americans in general.