What does childbirth have to do with it? I thought that's what condoms were there to prevent.
As far as emotional maturity is concerned, you're still engaging in special pleading. What makes a 17-year-old "mature enough" and a 12-year-old not "mature enough". Lemme guess: the fact that you're 17, right?
Call me back when you're 27 and tell me you haven't matured a whole lot, emotionally, in those intervening 10 years.
So. An 18 year old. Cannot handle sex better than a 12 year old?