Talk to your nearest RAF Careers Office (AFCO); ask them what other qualifications would be considered equivalent to 5 GCSEs and 2 A levels- such as HND etc and what they would accept - then you could embark on a three year course in a subject such as engineering for example, or a subject that interests you, and use that as the entry qualification and still be only 21/22 years old and well within the age limit. At worst you can re-sit your GCSEs and go for the A levels you need. You are under no obligation by visiting the AFCO and don't be put off by the Recruiter as they may try to encourage you to apply for a ground trade that they are currently short of and tell you that you can always re-muster (this did happen to me but I still applied to fly and succeeded) The age range for in-service pilot application is 26 and you can get educated to the right level by the service but that is a very hard route to follow and to be considered only as a last resort. In addition, consider joining a local ATC Squadron as a civilian instructor to start with while you are studying; this will give you a good insight into service life through visits to stations - and a chance to fly! Look at the attached link for more advice on the application process at OASC and how best to prepare.
http://www.oascprep.co.uk/oasc_introduction.html
Best of luck in trying - if you are determined enough, and good enough, you will succeed!