[Les Paul]

As an ex coach 30+ year weight lifter and have been to clinics etc. No heavy dead lift, squats with heavy weight unless there is a machine for it. Besides those 2 things, not likely he is strong enough to hurt anything right now. How much could he bench press right now? Some of you guys think he is going to go in there and start benching 200. Not going to happen. It certainly won't stunt his growth either.
Have him do circuit training with lighter weights and higher reps. 3 sets. All that said starting him out on good old push ups, sit ups, chin ups to get him started is a wise decision. If you don't want to go to the big bar stuff or want to hold off till you see he is committed use free weights. It teaches proper form and balance. Good luck. I started with weights when I was 10 in 1964 still like it.