If he does want to work in the games industry, skill will take him far, further than any computer game course that a university or college offers. Languages is a fantastic one which is much in demand, or the ones with more competition: graphic arts including CAD and 3D digital sculpting, "real life" art/sketching, coding/programming skills, ability to write a decent storyline or compose music. If he is aiming to do some sort of course then it's best if it has links to industry, other than that he'd need to get out there, be active on forums, volunteer, apply for tester positions, offer to do unpaid intern work, apply for jobs abroad as well as in the UK - this is where the language skills come in too. The computer games industry in Germany for example is thriving and growing, due to tax breaks for this particular industry. There are loads of software and hardware companies here, games, components, all sorts of things.
In addition to that there are tournaments now, there is such a thing as E-sports which is where players compete on the games worldwide for huge cash prizes and sponsorship. Games aren't just a soul destroying, mind-mushing thing any more, the potential is real and it is probably larger than you think.
However I also think everyone's suggestions on this thread are great about bringing in his interests from the game to real life. Or from other games - Civilisation for example could lead to interest in history, he could look at modding games to teach himself coding (usually not allowed in MMOs) you could look at tabletop games if he is into fantasy etc.
I also think the idea of him earning his time is a good one. This enables you to ration it but him to keep some control over how much time he gets to play. It also fits in with real, adult independent aims - he will one day have to juggle the game with finding a real job, if he wants friends in real life or a girlfriend etc, he will need to balance that with his need to play the game. It's all good practice.