I don't think that you can afford not to have GCSEs, so get on with those.
As time and money are there (and frankly, if you want this enough, you'll find both) build up the flying hours towards your PPL/fATPL.
And apply to the RAF as/when the opportunity occurs. If you succeed, put the civvie flying on hold, but services recruitment takes a while anyhow and they'll have much more regard for somebody who is clearly trying hard and covering all the bases.
G