People forget that Aerie is a (surface) elf; elves mature at a slower rate than humans. However, Underdark drow - despite also being elves - are forced to mature quickly thanks to their dog-eat-dog culture.
I think you are switching two concepts here ... Its one thing when your body transformation is finaly complete ... you stop growing ... and therefore you are physicaly mature. And its another thing, when society is forcing you to take rights and responsibilities ... and therefore since that moment you are concidered mature.
I dont quite see any conection to models that are used for Baldur's Gate elves tho.
If my comments bother you, there is nothing easier than telling me to stop. I mean ... I won't ... but it's easy to say.