As a parent of a gymnast, I was once concerned about these topics and did do a little research. First, like many parents, I didnt enroll my daughter in gymnastics because she was short. I enrolled her bc she was a toddler swinging from my canopy and attempting any move on the furniture that may have simulated flying. I gave no thought to how tall she may grow to be. In many studies that I have read, delayed puberty only occurred in gymnasts that were training more than 30 hours a week. This is not your general USAG kid. This is the schedule of an elite or maybe future elite athlete, and I beleive you would find the same delays in elite swimmers and other athletes of that level. I have seen taller than average (5'8-5'10) high level gymnasts in the USAG program, and they are succesful. I think they must have a really strong work ethic and a determination to overcome the obstacles that face them because of their height.