The very long winded way of joining the RN as a pilot is to join as a rating, maybe Air Engineering Technician if you're into that sort of stuff, then getting your qualifications from Petty Officer Qualifying Course and then going the Upper Yardsman route. As I say, this is the long winded route but is achieveable. I'm not sure what you get out of the PO Qualifying course these days but it used to be enough to get you to the AIB. You need to start cracking early though as most blokes who join at 18 and go this route are getting close to the upper age limit when they finally get to Dartmouth.
Or if you've got time just do what everyone else suggests and get the required points before joining, surely you'll get something from your training to be an Aircraft Engineer?
Good luck