Just on a technical note, the earlier onset of puberty is often attributed to better nutrition. If we look at 'back in the day' when the onset of puberty was later, it was generally considered that food is food. Nowadays in the first world nations a lot of emphasis is placed on a balanced diet and getting the right nutrients into your body. This seems to have a side effect of causing faster and better physical development. The whole 'hormone' thing seems to be largely scare-mongering as far as I've been able to determine.
Also,
this. A five year old gave birth in 1939 to a healthy baby boy. The idea of early development isn't entirely new, although this is an extreme case. My girlfriend had breasts at 9 that were bigger than those of many grown women. These things happen and have been happening for a long time now.