Gliding
Thats a real big question wannabe and if you really want to find out then your best bet is to go and have a look at the operation as all clubs operate slightly differently.
Initially you could have a look at the London Gliding Club website and see what their rates are.
And though it may appear to be an old folks sport it certainly is not and we have a big Junior movement with solo pilots as young as 14 and the Junior classification continues up to the age of 25.
Best of luck.