Having been an airline pilot most of my adult life, I'd recommend the attached article, since it covers the basics. Obviously, this applies to the industry here in the U.S., but there's not a
lot of differences with the U.K. rules and requirments.
http://travel.howstuffworks.com/pilot.htm
About a third of the way through the article you'll see a discussion of experience. Obtaining sufficient experience to actually be considered for employment has
always been the bigest difficulty. For a dedicated individual, the actual hands-on flying skills are very interesting and most people keep "with the program"... However, after attaining the required certificates (their called licenses everywhere else but the U.S.) trying to find minimally paying jobs just to achieve experience can be disheartening and there's lots of routes to that goal.
Education is an important consideration, but, generally, a sound liberal arts degree will suffice. There's little in the way of really necessary mathmatics or physics courses that have precise applicability, for example.
The cost of flying in Europe or the U.K. is quite high in my conversations with pilot's from those areas. The cost is considerably less expensive here in the U.S. and we see flight schools dedicated almost exclusively to training foreign students here. It's such an expansive subject that it can't be covered adequately in this limited forum, but I certainly encourage your son to pursue flying... I wouldn't have missed it for the world, most of which I've had the opportunity to view from the left front seat of a Boeing 727 (or other fine aircraft) at 35,000 feet...