I think, to some extent, that they need to start aging the sport up, or give up and call it "girls' gymnastics." On the other hand, obviously, there's an advantage to being young.

Of course, the younger ages favor totalitarian countries with sports machines that pick up three year olds and start training them, so they're at their peak at thirteen or so. Take a country that can't enforce this and doesn't have the authority to just grab a kid, and training will start later. (This isn't just because the government can't do it by fiat--there's a different culture, which says that children perpetually have a choice, and toddlers don't have a naturally great attention span. By the time they're school age, we're more willing to say, "Hey, stick with it," but even then, we're more likely to let them out if they feel like it.)

My bigger problem in particular is that, arbitrary rule or not, some teams are following it and others aren't. Maybe we left a really talented thirteen-year-old at home. Maybe Japan did as well. Which means that China was using its entire resource pool for talent, while we restricted it.