While I personally find tribulus pretty awesome at sub body-building doses (it produces a mild, fairly long acting, stimulant-like buzz), fucking around with your androgen receptors and your pituitary gland in your teens is probably a bad idea. While there's a fair amount of research regarding its traditional use to treat infertility and sexual dysfunction issues and the research reveals no significant issues relate to that use, there's not a lot of research into the effects of taking it long-term in high doses (there's one study which found it produced dopamine fatigue in sheep - that's far from definitive but it's consistent with the effect that long-term, high dose stimulant use can produce in humans so further research is warranted).
Oh absolutely, and you're right there's not a lot of research surrounding tribulus at all (in fact I don't even think it's been medically proven that it has the effects most people consider it to).
You're 100% correct though, and I'd go further that unless he's got a reason to there's probably nothing good going to come from a 17 year old taking anything remotely related to hormones except under the direction of a decent doctor. A good diet and exercise is probably going to have the same effect (and less side effects) for someone up until their late 20s at least.
