I found myself in this situation some 20 years ago. Passed the aircrew medical three times (test in advance, flying scholarship then the actual aircrew selection tests), all the while wondering if I'd be found out. I even ticked yes in the hayfever box. The RAF offer was a General Duties (ground) commission to see how the breathing went, on the basis that it often clears up post-puberty, when I could re-apply for flying training after a couple of years. Trouble was, it rested on my conscience in case I let anyone down and when the letter turned up saying" turn up at Cranwell next March" I politely declined. I've often wondered since whether I did the right thing or whether my opting out meant I lacked the right stuff anyway.