Here are the requirements to join as a pilot in the RN (taken from the RN website):
Qualifications
180 UCAS points (including 2 non-overlapping subject areas with each subject must allocated at least 45 UCAS points) and five GCSEs (A* to C) or Scottish Standard Grades or equivalent, which must include English and Maths.
You’ll also have to pass flying aptitude tests at RAF Cranwell.
You must be aged from 17 to 23 years (under 24 years old when you begin basic training)
180 points is equivalent to a B and a C or 3 Ds at A-Level. Points win prizes!
I recommend cracking on and getting these. If you join up as say an AET with the aim to get a commission and fly, how do you know that you'll pass the aptitudes / AIB? You may end up wasting a few years in a job that you don't really want.