Firstly if he has a computer I'd recomend he get MS 2000 to keep him happy for the next few years - it's surprising how much you can learn off it.
Secoundly I would advise him him to continue education until at least A-level and then either look at sponsership / self sponsership /University course. Self sponsership is very expensive about 50K for a CAA/JAA approved school to take him from scratch to a full Commercial licence in about 12-18 months.
In the mean time joining an Air Training Corp or CCF is an excellent way of getting airbourne for free - I did it for a couple of years and enjoyed a few hours flying aerobatics in a Chipmonk. Any other flying activity he can get involved in is good - sponsers often like to see a track record of enthusiasm.
Lastly it is possible - I was in the same position when I was 15 - it looks impossible , but 5 years on I'm about to start my first airline Job. Good Luck to him.