I suspect the increased inclusion of soy in many food products has contributed to early puberty.
http://www.scientificamerican.com/article.cfm?id=soybean-fertility-hormone-isoflavones-genistein
http://www.soyonlineservice.co.nz/articles/children.htm
And, naturally:
http://www.freerepublic.com/tag/soy/index
I’m putting my money on soy and the use of hair products that contain mare’s placenta.