Thank you for all your responses. I do feel that there is only a certain amount of information a 14 year old will process regarding nutrition and weight gain which I am not sure he is ready for. His trainer is in his early twenties and he listens alot better to him than me. It is just very costly to have a trainer with him every time he works out so I am trying educate myself.
I don't think he has made the connection that in order to develop more muscle that he's got to eat like he trains. It sounds like from everyone is saying the weight gain is easier comes a easier when he's further thru puberty. I am just afraid if he doesn't eat enough it will negate any gains that he is attempting to make. But establishing good form and technique early is important.
Regarding flexibility he hates to stretch but he is also hypermobile in certain joints like me. (elbows, hips and shoulders) This makes strength training more important for stability reasons as well. I learned this the hard way. Has any one else dealt with that issue?