Speedbird,
I am ex Navy, non flyer.
I say go for it, even if you dont make air crew, which is very tough, the experiences, training and friends that you make will stand you well whatever you choose to do in the future.
Ex military nearly always stand above everybody else when interviewing in civvy street. Get yourself a well paid job and do it yourself. Well thats my plan.
Everbody knows the RN is the senior service
and its the place to be at 18 years old.
Good luck and I am sure you will love it.
1ZA