That is something you should really ask a doctor about. Or you can just make an appointment for him.

Ya, you have not really made it clear what the situation is. Does he get hard?
I guess if he had to try viagra he was not getting hard. If he doesnt get an erection, there could be a few reasons. It could be a psychological problem or it could be medical. The most common medical problem is lack of blood circulation to the genital area (for which viagra should help).
Now if he does get hard but doesnt ejaculate, I would think there is really something wrong with his testicles or with his prostate or seminal vesicles. If you were to say he ejaculates but not much, I would suggest to try some herbal remedies. But if he never ejaculates at all, its more serious and you really should have him see a doctor for this.

Sorry I couldnt help you with first hand knowledge as I never had the problem myself. But your bf is still young and the problem should be correctabe.

I hope others can help with this.

Maybe ur bf is impotent, is that his condition since teenage, I mean is that inborn? If it is not, u must consult to a doctor.