Hello concerned parent, i read through the history and understand your concern. i wouldnot suggest using extra supplements for gaining mass or muscle,if he has adequate nutrition through his diet.specifically the protein and good quality carbohydrates. i would recommend 1 g of protein per kilogram of body weight for a healthy 16 year old boy looking to put on some muscle.egg,soya beans,nuts,milk etc are good sources of natural protein. a single egg white can give approximately 3g of protein.so a diet plan is required. renal function test should be done to assess function of kidney before having high protein consumption. he can add a quality protein supplement if he is looking to go for a championship or bodybuilding event.most supplements available today are of low quality or adulterated.so i would discourage that and for the workout routine ,i would advise it to keep it under 1hr(45mins to 1hr) ,2hour would damage the muscle and tendons and he would injure himself.Short effective training sessions i would advise and keep expectation of 5-10kg over a year. ask him to stick to the above points and dont overtrain.diet and rest are important than the exercise in putting on muscle i hope i have clarified your doubts and have a good day.please follow up if needed further advise.