Jambone,
You have time on your side.
Which is a good thing. The question only you can answer is what sort of career do you want?
Do you want to go straight from full time flying school straight to a RHS of a jet but potentially with a massive debt and a contract that is more like indentured servitude? (see the easyJet MPL thread...)
One of my colleagues was a BA cadet, did 13 years with them and was bored silly. He went to GA.
Or do you want the opportunity to do "other" things with your flying before pitching up to the airline offer (if ever?)?
Whichever one you decide, work hard at getting the best A levels you can, do some team sport stuff (good for leadership and working in a team etc).
Then get a job for at least a year. Do any thing that earns money. This will teach you the value of labour for pay. This will help you realise when employers are taking the p!ss, a very useful skill to have in the aviation industry.
I'll hold my hand up and say I am a bizjet pilot and love it.