Hi there and welcome to the forum!
Well, regarding your question I found the answer on the BA "Future Pilot Programme" website (see link at bottom of post):
You will need:
- 5 GCSEs at Grade C or above, including English Language, Mathematics and a Science (single or double award), excluding General Studies.
PLUS
- either 3 A-Levels at Grades BBC or above, excluding General Studies.
- or an Honours Degree at 2:2 (or higher) or a pass (or above) in a higher degree such as MSc, MA, MPhil, DPhil, PhD, MBA.
If you are interested in aviation and becoming a pilot, some flight schools and/or aero-clubs offer so called "introductory flights" duration is usually about half an hour and you can even be on the controls yourself, that'd be a good opportunity to get a first impression of what it feels like to fly an airplane. And if the airplane is a four-seater (like a Cessna 172, Piper Arrow, or even a Cirrus - very fancy airplane) your parents, or at least one of them could come along on the flight.
If you like it and if it fueled your ambition of become a pilot you could start working on your PPL (Private Pilot License) anytime soon, but the earliest you could take the check-ride would be on the day you turn 17, the consent of your parents provided of course. I believe I pretty much got you hooked-up for a family trip to the next airfield.
Once you got your A-Levels and you still want to become a commercial pilot, I'd recommend to try to get on an airline sponsored cadet programme, that's the best way to get into the cockpit. British Airways is running a so called "future pilot programme" for further details see the following link:
British Airways Future Pilot Programme
Best wishes and success for your future!