I was in the air cadets, joined at 13...but wasn't for me in the end.
I invested my Uni savings ( A choice my parents made for me not ,myself) to help in the aquisition of PPL, started training when I was 15, flying once a month...and doing ground exams...then solod at 16, flew more frequently and got my licence at 17, did a year of flying on my own, not much but enough to enjoy, and applied to Air Atlantique cadet scheme when I was 18...and was lucky enough to get it with only 60hrs behind me. So it can happen. :-) AND....as for schooling....I know its important...but I was pretty average on that front. Nothing special....its having the motivation and passion for flying I think helped in my case.
All the best anyway!!!