As for worring about him jelqing, in his developement stage, I would say that this would be the right time to start, maybe earlier? His body is full of testosterone, which converts to DHT!! DHT is responsible for the growth in the genital area! So he should take advantage of it now, and try to gain as much as possible during this time!If not he will end up like so many of us here, struggling to try to make minute gains! Saying that, you can gain either way, but in my opinion, you would have the advantage, and easier time if you start when your body is still growing. You only have to read some of the postings by Supra, about IGF, DHT cream, etc to learn that taking such drugs will put the body in a growth state(much like puberty), which is prefered if you want to gain alot. If it is happening naturally, like your brothers, then take advantage of it, the natural way!!