Was gymnast He Kexin (何可欣) old enough to compete?
This new post, from the Stryde Hax blog (search engine hacker), does an impressive technical job of finding information that has not yet been removed from caches of official Chinese sites. At face value it makes a strong circumstantial case that one of the gymnasts, the double gold-medalist He Kexin, was born in 1994 rather than 1992, making her 14.