Thanks SM for the reply!
Though it is just theorizing, the theory would not really match with Alien Isolation where all the xenos are domed and a queen is supposedly present, plus they're older than the xenos in Aliens which just throws out the age theory..
I'd just like for a more concrete explanation for the difference, James Cameron in Aliens said it was age, A:CM and other sources said it was casts ( I like that idea the most), A:I just added more to the confusion not explaining anything even though I love the game.
Who knows, maybe it's the environment?