Go with natural talents and real drive. There's no reason to complicate the various failures we all experience in life along the way, with having more people complicit in making core decisions that should be our own.

Of course, that's from the perspective of someone who did allow her parents to convince her that there was no future in art. The money I make in the misery of a career I've become stuck in is no comfort; I personally wish I had gone ahead with my own instincts, because (a) they were patently wrong that there is not money to made in art, and (b) I'd have been perfectly happy with less money while not doing work I really really don't like at all.

Maybe he can strike a compromise? Not make math his major, but just include a few math or business classes, that would help to support success in any chosen field.