I will preface this post by saying, there are a lot of different views out there regarding the proper age to begin strength training, and many people claiming to know what's best. I am not going to be one of those people, but I would rather like to give my opinion toward the subject and you can take it or leave it for what it's worth (I look forward to hearing your comments).
I do not believe there is one particular age where athletes should begin working out using weights. I think it is very obvious that young people develop at various speeds and different chronological ages. Therefore, I think the only generalization that can be made in this instance is that a young athlete should begin a controlled and moderated weight training program somewhere around the onset of puberty. What I mean by a controlled and moderated program basically means under the guidance of a certified coach that will effectively be able to teach and progress the young athlete appropriately.
With that being said, I think an athlete can begin strength training using body weight exercises at any time during their careers. This includes anything from push ups & planks to chin ups & squats. As long as the athlete is moving their body weight through a safe range of motion, I believe the exercise will be performed safely.
Now we've all heard the effects of lifting weights at an inappropriate age: everything from damaged epiphyseal plates (growth plates) to your hair turning green and everything in between. I'm not sure we can strictly adhere to these beliefs, especially the green hair one! This topic will be argued based on the safe range of motion principle again and I'm not sure if there is any evidence that has shown young athletes become injured from weight lifting in a safe range of motion. Problems typically occur when they lift too much weight, demonstrate improper form, or do not follow safety precautions in the weight room. So people will argue that you can weight train by gently loading at an earlier age than puberty, my opinion just likes to error on the side of caution as I would never want to negatively affect any athlete's career.
Thank you for reading today, tomorrow is another Wednesday Review Day!