The youngest mother I have heardof was an Indonesian girl who delivered a healthy infant at 68 months of age. She was not even six, meaning that she lost her virginity at five years of age.
The onset of puberty is the onset of potential pregnancy. That is why it is so wise to keep your virginity until your wedding night.
I blame the steroids and chemicals in our foods for pushing puberty to an earlier and earlier age. You are what you eaty, and all those substances foreign and artificial to food have GOT to be doing something.