Okay, I'm not an expert, but this is evolution, right? In nature, the girls who had their periods early and could become pregnant before their bodies were really ready for it will die, slowly leaving the girls who had their periods later to pass on their genes, so eventually they outnumber the girls who gave birth early and lived.
That is, in fact, how nature works. I have no idea where the "nature will take care of everyone" idea came from. Nature has no problem killing you off.
