I've had some really interesting replies on here to my original question, so thank you all very much for taking the time to reply. Yes, he's still very young of course, but we're just thinking ahead to give us some idea of what action he should take when he's older. We live in Colchester, Essex so would it be a case of applying to our local network?
This thread has certainly got me thinking. The membership of the forum seems to be predominantly younger enthusiasts, but with a few of us that are actually working in the industry, including drivers. I am sure many on here are asking themselves the same questions.
As you will have gathered, there is no guaranteed route into driving; no job in the industry is a prerequisite for it, and none particularly equips you either. All trainees undertake the same training, regardless of what they have done before.
At 15, it's difficult to judge where his aptitudes lie. The selection process is aptitude based, ie you've either "got it", or you haven't. There is also a structured interview (see other threads here), which draws on your experiences to date. That can be very tough for a younger applicant. I wouldn't have passed that at 21. At 28 when I took it, I was just talking about going to work.
There are plenty of other options within the industry that he should consider. Network rail run graduate and apprentice training programmes (engineering mostly), the big transport groups have management training schemes, and you can have a very good and lucrative career in the various maintenance disciplines. Operationally, signaling pays well, and offers an interesting and challenging alternative to driving. If he likes being around people, he may be better off as a guard, which again is a good job in its own right. Many of the best guards that I work with, have no interest in driving. It requires a very different skill set. Driving is something that a lot of us have come into by accident!
If he's an enthusiast, or is just looking for something worthwhile to do in the summer hols, I'd suggest that he has a go at volunteering on a heritage line. The actual "railway experience" won't count a jot, but he will find out if he's any aptitude for railway work, and whether he likes it or not. It's also a good way of learning general workplace skills, and will aid his maturity, as he will have to prove himself in an adult environment. That will help, whatever field he eventually ends up in. I'd recommend one of the more established operations - North York Moors, Ffestiniog, West Somerset, etc. I know there are all a distance from you, but they all have accommodation, and a working holiday (16+) could be very beneficial. It's something that I did as a teenager (and still do), never thinking that I would end up on the footplate for a living.
I've every sympathy for those above who mention talented youngsters stuck in duff jobs. Been there, done it after graduating in the middle of the last recession.