When I was in middle school (probably around 12 or 13) I wanted to get into working out and lifting weights, but my gym teacher told us that it would stunt our growth. My friends ignored his warning but I took it seriously and didn't lift a weight until senior year of high school.
Lifting weights will not stunt your growth. Arnold Schwarzenegger started lifting weights at age 15 and he’s 1m82/6’2″. Lou Ferrigno and Dave Drapper also started young but are over 1m80/6″ tall. Same with athletes like Shaquille O’Neal, David Robinson, Karl Malone and Michael Vick.
This myth probably started in the 80s with Olympic lifter Naim Süleymanoğlu aka Pocket Hercules. He was only 1m47/4’10” but could lift +180kg/400lb over his head. Some people concluded the heavy weights stopped him from growing…
The main cause of stunted growth is malnutrition. Outside of that your height is mostly genetically determined. You’ll keep growing until you’re about 21, regardless of lifting weights.
Lifting weights is good for teens. It builds discipline and improves work ethic that helps with studies later. It gives them a healthy lifestyle that keeps them from unhealthy ones like drugs and drinking. And it gives over-active kids an outlet for their higher activity level that beats taking pills.
The key is to start light. Get a 5kg bar or even a broomstick. Focus on proper form to build good habits and avoid injuries. If it’s your kid, supervise him every workout to check his form (make sure you know proper form). Praise him for good form and discourage bad form immediately.