you dont lift 40kgs on one arm mate, some body builders at my gym obly do 50, and there 20 to 30 years old
man i will give you my own experiance lift light weights not heavy for you, and the most important thing is the form and the technique of the exercise. cause bad form will cause you injuries and engadge your height
I understand your concern but it is totally okay to let your son train with weights because it will not harm any of his development and it will enhance his growth too in fact its best or teenagers to life weights often .
I'm 17 and taking testosterone supplements because of delayed puberty. Recently I've started lifting weights and exercising a lot more and was just wondering if weight lifting would have any negative effect due to the delayed puberty?
Thanks.