It seems like a good first step would be to set the minimum age to compete at world championships or the olympics at 16 or 17 or maybe even 20. Then delaying puberty wouldn't be a thing because everyone will have passed it.
Delaying puberty will still be a thing because people that end up competing at the top levels start training intensely long before they are eligible to compete.
Its not like someone wakes up one day and says "I think I'd like to be an Olympic gymnast", trains for a few months, and competes at the Olympics.
That's above the median adult female height in many countries. And gymnasts (even at full adult height), of both genders, tend to skew short.
Anyways, just because some participants may cheat doesn’t inherently mean a rule isn’t worth making.
Athlete's do doping checks all the time. Might as well do a single-time age check as well.
They do age exams, looking at various physical features, but it's fairly error prone and not that precise.