When I was young I weight trained like anything and never put any muscle on if truth be told

, it was only when I got to 17/18 it made a diference. I think my body shape at that age was to be skinny and athletic.
So now my son at a similar age (14) wants to go to the gym with me and weight train. He is incredibly athletic but as skinny as a rake. I think its too young.
Any advice? Weight training too young a waste of time?