at what age should one start training? I would like to help my

No heavy lifting until at the earliest 15 I would say. Before that body weight stuff

>>41775369
1)Keep him constantly active with things like hiking/running/playing. Indoctrinate him with the mindset of self-improvement, maintaining a positive mindset, and working hard.

2) Encourage body weight exercises like push-ups/pull-ups around 10-11; engrain exercise into his mind. Remember, he has to want to/enjoy exercise for this all to stick and help him.

3) low-weight form training at 13-14; benching just the bar, bodyweight squats, etc. to teach form and introduce to lifting (don't want to start heavy weights while bones are still developing)

4) intermediate weights at 16

5) 17 begins the journey to leave humanity behind.

play intramural sports and fun physical activities until probably 14-15 once puberty is in gear, then an introduction to novice weight training would probably be good to start