I'm just in the pilot grading phase with the RN. PM me with any questions, but don't be put off by any comments that suggest that high competition should stop you from applying. A guy on my course (pilot) has two D's at A-level, and a lot of my friends in the RAF (pilots) failed a year at university. Yes, competition's tough, but that's because it's a fantastic job - any fantastic job will involve beating a crowd. At 19 you've got oddles of time, just get on with it.
Good luck, it took me 3 attempts.
Fanois