Haven't read... MOST of this thread... so forgive me if I'm ignoring anybody. I think DLD has the right idea. Make the information available to them, let them make their own decision.
I would have KILLED to know about this stuff by the time I was in my early teens, but if the kid doesn't want a bigger dick there's plenty of other constructive things to go after. :D
I'd probably want to be as sneaky about it as possible. Leave some reading material out where he can 'find' it. Let him think he's discovering it all on his own. But that's just because I don't want to talk to my kid about his wang. (drunk)