This is actually the first time I've heard or read about this, as I haven't really been following the Olympics that closely. Yeh, shame on me.
In a nutshell, it has been alleged that certain Chinese gymnasts at the Beijing Olympics do not meet the minimum age requirement of 16 set by the IOC, and are actually 14 years of age.
A blogger, Stryde Hax, did a little research of their own and came across some official documents, cached from the General Administration of Sport of China web site, that appear to back the allegation, and has posted some screen shots of their research in the event that the cached documents suddenly disappear, as the original documents already have. You can read the blog entry here. Check it out and decide for yourself. It certainly reeks of something, and it's not sushi.
Also, as requested, I have taken a couple of screen shots and posted them here. The more the merrier!
You can also read a little more about the controversy on He Kexin's Wikipedia page.
Why isn't the IOC doing anything about it?