Being a teen myself, I would say monitor him and just keep back for now. Eventually you will need to have a good talk with him about AAS (if you havent already) and start guiding him to doing it correctly. I bet with your knowledge, you could tell within a week if your kid is doing anything other than gear, protein and creatine. Guiding him now would definitively send the wrong message that roids are ok at this age, even if you said "roids are not ok at this age", actions speak louder than words. The placebo effect is also a great idea for a while down the road. Get a bottle of Beast, empty it, fill it with BCAA pills and say "this is the real deal, its nothing to play with". ask him if he thinks he is ready. if he says yes, give him the bottle and tell him he'll be dead if he says anything to anyone. the power of the mind (and slightly the BCAA's) will have a wonderful effect. This is one of the biggest decisions as a parent as it will ultimately decide his future (test levels, a girl who will put up with possible TRT down the road, difficulty stopping cycling). Trust yourself to make the right decision.