How could they do that? Being an honest host and all, and abide by the regulation and standard set by the I.O.C.? But with nationalism, pride and arrogance seriously endangered, a little bit of Chinese tweaking wouldn't hurt at all. Especially after miming at the opening ceremony, you would have thought Beijing would have learned a lesson. But, hey, if they can go by once without suspicion and detection, why not do it all the way? Especially considering the advantage of being the authoritarian host. Cover-up is just a piece of cake and could happen without a stir from the critics.
Why do they cheat? I seriously doubt on the effectiveness of cheating when you consider China trains its athlete as young as 4 on his/hers designated sport! In any case, Beijing may have not rigged the Game, but then someone is saying otherwise.
Is He Kexin really underage? That would be extremely hard to prove, given it is "a walk in the park" for the authoritarian regime to rigged the Game. Truth shall be told, 20 years from now. Just like the good ol' Soviet days when taking steroids is a sport. :P