I would suggest get into the local RAF Cadets, even if you have no interest in joining full time, as you can often get flying hours as part of that.
Also consider engineering type careers (if you are interested in it) as it can lead to doors opening at a later stage. Basically plan to have a career outside of the cockpit as well, because it is incredibly difficult to get in at a young age.
Other than that, unfortunately you may be waiting a while given your age...unless your parents have a nice big house and you can get access to a loan of around £90k!