Keep in mind the puberty aspect works very different for girls then for boys. A well nourished boy that practices sport or exercises regulary will look younger but hit puberty normaly. Girls largely depend on hormones (even more so then boys) to develop me thinks, and nourishment plays a pivotal role in how much hormones you can produce (along with genes of course).
I believe I've pretty well nourished throughout me life and I exercise regulary, and me doctor(s) aways say I have the body of a teen, and I'm 20. I've met people my age who look alot, ALOT older.
Given the fact that girls aren't relegated to secondary roles anymore, get more attention from their parents and so get better nourishment, plus the fact nourishment and hormones have a greater effect on them, its only natural that they hit puberty much faster then boys. Its getting scary though, while boys today are definitely hitting puberty earlier, girls are hitting it much earlier. I've met girls around 10 and 12 that look like 16 year old girls.
If you look at old pictures of young girls that age they barely have any resemblance with today's girls of that age.
And yea, China is a pretty weird country, but thats mainly because they're leaving the rural state phase behind and going towards full fledged world power really really fast. Old customs are still around, and now that the country has opened itself to the word we can see the clash of the old customs VS globalization. Hell, there are several ongoing investigations in certain areas of china to stop the commercialization of aborted foetuses, because according to an old chinese custom, eating foetuses makes you younger and beautiful. Want another one? Eating placenta is even more common in large areas of china, they believe it is great for the skin and makes your children strong if you feed it to them.
I'm not joking, look it up.
@smjjames: Its not that they do it for population control. For thousands of years baby boys were aways much more valued by chinese family then girls. A family that gives birth to a girl will even sell the baby to richer couples that cannot have children, and keep doing so untill they bear a son. This is because the chinese society is largely patriarchal and only boys can inherit the family's belongings.