"He hasn't got a grade in anything yet! It's still new to him but his teacher is very encouraging and reckons he is one of the most promising music students in the year. He has played guitar for about 2 years now, and drums for a little longer. He has also picked up DD's uke that she asked for for christmas a few years back, and has rarely touched, and was playing it really well straight away. This is what confuses me - until a few years back music was just something he listened to"
OK here's my honest opinion (as a musician and music teacher):
At his age, and with such little experience behind him, it's too late for any question of a career in classical music. Absolutely no chance. People just don't pick up instruments out of the blue in their mid teens and end up in professional orchestras or string quartets. Sad, but true.
The same is not true of non-classical styles of music (which let's face it, account for 95% of the music industry). People DO, all the time, take up singing or strumming a guitar in their mid teens, find they have a flair for it and, with passion and grit and determination, end up forming successful bands or producing successful records. So if it appears to be working for him, by all means encourage it, in this respect.
But here's the thing: the academic route of a university or college music degree is absolutely 100% useless for anything except a career in classical music (and university courses are pretty useless for the performing aspect of even that). If he wants to play in bands, write or produce songs, run a record label or anything else, then he needs to spend the formative years of his late teens and early twenties out there doing it - learning how things work in the real world, and above all meeting people, lot's of people. Not sitting in some university earnestly discussing the harmonic procedures of Jimi Hendrix and imagining it's going to get him somewhere.
The last decade or so has seen a proliferation of popular-music based higher education courses. The vast majority of these are of no use to anyone, and are really just a cynical exercise in getting bums on seats of universities. There might have been a slim case for them when higher education was free, and a university could be the structure within which to meet like minded people, talk a lot of shit, take a lot of drugs and try some creative ideas out for three years. But at 9K a year, that becomes a hell of an expensive indulgence in navel gazing.
These courses routinely take students with woefully inadequate technical skills who stand no chance whatsoever of ever working, simply so they can fill their numbers. Many of them are focused around music technology and sell themselves as a route into "working in a studio", which is a job that effectively doesn't exist any more. You might as well do a degree in penny farthing maintenance.
The only use in doing such a degree would be if he specifically decides he wants to be a music teacher in a secondary school, and intends to follow it with a PGCE. Since you haven't said that he's either mentally retarded, masochistic or insane, I presume this is not the case.
Now don't get me wrong: I meant what I said about encouraging music if he's good at it and loves it. But don't try to do it by wasting three of the best years of his life on a degree. He needs to get a sense of what he wants to do with it, and then go out and DO it. Leave school, form a band, write songs, set up a home studio, and wear out shoe after shoe going around selling himself to anyone he can corner for long enough.
OR do a degree in a completely unrelated subject, while doing music on the side, with a view that it might take off or might not. This is a path often not considered by obsessive music types but you'd be surprised. One of the best violinists I ever met, who is now leader of a major orchestra, has a maths degree from Oxford. One of the most talented kids I ever taught is now at uni doing marine biology, while gigging every week and selling CDs through his website.