If somebody from an unknown country begin to play CHESS, it is not a reason to change the game and add units from than unknown country. It is the same with Aoe 2.
See, what I find an read here. It is from a forum for Aoe 4.
Click over ““Aztecs, Mayans, and Incas”” to open the link.
So Historically accurate will be if South american and African civs reach only Feudal Age at Aoe 2.