I can't imagine having to start puberty so young. I read years ago that bigger girls tend to start young, so when my girls were born I made a point to make sure they had a healthy diet and got plenty of exercise. I always struggled with my weight, and I didn't want them to not only have the same problems, but maybe have to deal with puberty early because of extra weight.
I also steered clear of hormone-laced milk, although I've heard recently that it is a myth that those growth hormones have anything at all to do with early puberty. Still, I do make sure our milk has no growth hormones.
Oh, and by the way, the girls are now 19 and 14; both are healthy weights and started puberty at around age 12. But I also wonder how much of it is genetic.