This may be a question more for r/linguistics as it deals more with that than recorded history. However, as someone who has some background with American Indians, I should probably point out that there are something like 50-100 language families and isolates in the Americas which have evolved over the course of 20,000-15,000 years, charitably it is more than 5000 years before we can even remotely reliably reconstruct the earliest proto-languages. Heck, some recent genetic studies have pointed to a 30,000 year divergence with people living in the Bering straight, though that seems...extreme. Since writing is a relatively recent invention in the Americas, at least as far as we know, our ability to reconstruct reliably is diminished so these language groups could be more related than they are proposed to be, but this is a controversial proposal to say the least. Furthermore, people may have come to the Americas in several waves, but this is another controversial proposal. In essence, I think looking for a proto-American language or even American language family is not really possible.