M.D. The best time for future Olympic athletes to start training is before they start puberty. Having large strong muscles makes you a better athlete, and starting training before puberty enlarges the bones.
Muscles growth is limited by the size of the bones on which they attach.
The larger the bone, the stronger the muscle. The larger and stronger your muscles, the harder you can hit a ball. Children who start to play tennis before they go into puberty have larger bones in the arm that holds the racquet. Their tennis arm bones are larger than those who start to play tennis later in life. Lifting weights during growth does not prevent children from growing to their full potential height.