I had this same discussion with another CB member (and I'm pretty sure it has been discussed over and over again) and I agree with her, that for us it is very difficult to guess an Asians age.
There are several things coming together in this point:
1. Chinese girls often have a different, more fragile and less muscular body type.
2. There is a careful selection at the beginning and through the girls entire gymastics carreer. Since small body types flip better, have straighter lines and probably work better with the Chinese gymnastics and coaching style, they are more likely to make it to the elite level.
3. Intense training (at a young age)+ different nutrition in the food = low percentage of body fat = smaller and leaner bodies.
4. In the Western world it is common for teenagers to make themselves look A LOT older via make up etc. We are used to different ideas of "looking grown up"
5. No guarantee on this one but I've read somewhere, that in Chinese tradition (mostly practiced in the poorer and rural regions) they have a different system of age counting, which begins BEFORE the child is born, so there might be "wrong" numbers on the birth certific