I only got into flying after I left school; if I'd mentioned it to my school careers department I think it would have put me off for life!
You do not need any qualifications in maths or physics to be a pilot. However, you may stand a better chance of getting some scholarships and sponsorships if you have them.
Above all, I would pick subjects that you enjoy and are good at. Good grades are good grades, whatever subjects they are in.
Try to get a flying scholarship through the Air Cadets, and as soon as you are 17 apply for the GAPAN and Air League Scholarships, as they can give you a great start to your career.
Good luck!
Al