If you have a real passion for flying, start now! Find your nearest gliding club and learn to fly gliders. Apart from the great fun of flying and the pilot skills you will learn, it is a great way to mix with pilots and gain all the insider knowledge. Many airline pilots (including very senior training captains at major UK airlines) fly gliders as well so the networking opportunities, potential references, tips about scholarships, airline schemes etc are invaluable. I used to fly and teach the youth group at Lasham (Lasham.org.uk), it's the biggest gliding club in the country and has a very strong youth team. It's also not far from London/LHR so many airline pilots fly there. The flying is very heavily subsidised and generally works out the same (if not cheaper) than any other extracurricular activity. I know at least 4 or 5 people who I taught gliding 5 or 6 years ago when they were your age who are now airline pilots.