Apologies that there are 4 comments/ questions responded to here - please find your relevant answers.
Firstly, I agree that at 19 you def have a LOT of time to get your academic quals in order to go for an Officer aircrew job so if you do really want it then go for it.
Secondly, The Navy does operate a different policy to the RAF. It's medical requirements are also less stringent but if you do have any 'defects'(sorry!) of a medical nature, each case is looked at on an individual basis. One of my oppo's was born with a heart defect which hasn't affected him for about 24 years (since he was 3), the RAF wouldn't take him, the Navy has....
Thirdly, Navy is (I believe) currently recruiting Aircrew, not Pilots and Observers. (Fanois, please correct me if this is wrong). So you apply for aircrew, go to AIB, join Dartmouth and then do both pilot and observer grading before being streamed one way or the other.
Lastly, both NZ and Aussie have do indeed have older cut-off ages for Pilot recruitment. From what I can gather from my time with the RNZAF/ Navy both countries are having such a hard time recruiting that they have simply had to widen the net.
Hope this helps....