What I wanted to know was what they had to tell the years apart. Counting seasons makes sense and I know fictional properties will sometimes say "she was 5 winters old" but that means someone had to keep track of that time. With writing being more difficult than jotting down a quick note then how did they keep track of ages and time?
For the Maya, they made use of three different calendar cycles. The shortest one was a ritual calendar consisting of 260 days. This calendar consisted of 20 unique day signs that repeated for 13 months. In conjunction with the ritual calendar the Maya had a solar calendar of 365 days. The solar calendar consisted of 18 months of 20 days with a five day ritual week to bring the number to 365. The interaction between the solar and ritual calendar produced cycles of 52 years that ideological significance.
To record deep time, however, the Maya made use of what we call the Long Count. This is a running total of time from the beginning of creation. You could think of it as an odometer on your car keeping track of miles, but for days and years in this case. The calendar was recorded in a set of five numerals, which we write as X.X.X.X.X. when we discuss it. Each position records a certain amount of time. Working from right to left you have the k'in which simply recorded days. When the k'in goes from 19 to 20, it resets to 0 and the next position over gains 1. That position is the winal, which records months. The winal only goes as high as 18, that is because the middle position, called tun, records years. As I stated above, the solar calendar consists of 18 months of 20 days and the Maya did not want to break that system because 20 is seen as an important number. The five special days, though, are not given their own tun number. The tun position, like the winal position, resets to 0 when it reaches 20. The second from the left position is the k'atun which records periods of time in 7200 day cycles (20 years of 360 days). The final position on the far left is the b'ak'tun which records 20 cycles of k'atuns, or 144,000 days (20 k'atuns times 20).
Using the long count system, today would be 13.0.3.12.2. which means since the point of creation 13 b'ak'tuns, 3 tuns, 12 winals and 2 k'ins for a total of 1873322 days since the point of creation.
But you may be wondering, when was the point of creation? That would be August 11th, 3114 BC. The earliest confirmed Long Count Date we have is at Tres Zapotes in Veracruz, which isn't even a Maya site. The date recorded is 7.16.6.16.18 or September 1st, 32 BC. There doesn't seem to be a gap or break in the Long Count used in Veracruz and the Long Count used in the Maya, which might indicate that this system was in use long before either culture but was not recorded on stone or on pottery. Perhaps it was written on paper or simply remembered by the priests who kept track of time. It's not like there was any large thriving civilization in Mexico at around 3000 BC. People were still very much in the process of domesticating plants and adopting agriculture and ceramics. So at this point we just don't know the why behind the start date.