A danger the future holds

Chemical doping has never been a big problem in female gymnastics. Mostly, because being physically fit, while relevant, is a much smaller part of the sport than it is for other sports (like cycling...). No matter how fit you are, you still have to train for long hours and your success will depend more on far subtler ability and skill than on fitness beyond a certain minimum.

But the issues you (and Goethe and d) mention make female artistic gymnastics one of the most attractive sports for "genetic doping".

You cannot give substances to a gymnast and ipso facto improve her performance. But if you could take an outstanding prepubescent gymnast and genetically treat her so that she doesn't grow overly tall and her puberty delays indefinitely, or at least beyond expected ages of Olympic and Worlds competition, then you would likely be engineering the Latynina of the 21st century.

It has already been said by the WADA that they will not allow "genetic doping" anymore than they allow chemical doping. But it's always been tricky to know how "genetic doping" could even be detected. In any case, the prize might seem worth it...

The problem here is that we aren't exactly sure, so far, what the effects would be of delaying puberty in that fashion, and what risks might be involved for the girl both during treatment and after it.

Age bans only make it all the likelier than in 20 or so years, for a gymnast over 16 (or over 18 or 21, as is likely to become) realistically to have a shot at an Olympic final, they have to be under genetic therapy to delay their puberty. Absent age bans, the temptation, while not entirely absent, would be considerably smaller.