Seriously what can the IOC do? They have Chinese passports with their age shown as 16. Apart form finding the passports fraudulent, there is nothing they can do. Can't go messing with legit passports.
YOU Walk right up to the honcho, show him the registration papers from past events showing their ages then, and their ages now, point out the discrepancy, and ask what's going on. Then call them a bunch of lying weasels and take their medals.
Well yeah they can do that. But what is more convincing, papers from a gymnastic event (oh that was just a simple error!) and a passport?
Cheating stinks. I'm not for it, but the IOC don't have no say over stuff like official documents.
Cheating using official documents (ie. government sanctioned cheating) sucks more.