Hi Superlukeyboy,
Well i remember having similar dreams to yours when I was 15! I'm now 30 and I didn't join the RAF due to bad exam results and not getting on at school. I'm now studying to be a commercial pilot before it's too late.
You want to get yourself up in a plane and make sure it isn't a romantic idea and that you enjoy flying, if you haven't done so already. In terms of G.C.S.E's you will need good grades in Maths, Physics etc.. Are you a member of the A.T.C Air training Corps ? If not join. A levels you will need ideally Physics or Maths again. My one bit of advice is dont piss about at school, knuckle down and get those exams results, it will open more doors for you if Aviation is your dream, hope you make it happen, all the best,
Dan.