I agree with busz. I am 17 and just finished my AS Levels. Focus on your GCSE and A-Level grades first, and it always helps to get some flying in whenever you can.
There are so many routes to take, that you need to look into all the options, and it depends on your finacial status. If your family are able to support you financially then paying your way into the business is a good option, but always keep a look out for any sponsorships. I would have a browse for sponsorships now over the net just to get a rough idea of whats out there.
Also start thinking about your PPL, because thats your first step towards becoming a commercial pilot. Look around for PPL sponsorships or schools that do PPL courses, if you can pay for it yourself.
Obviously I'm not a commercial pilot, but this is just one option for you which I think is quite a good one. Other people will have other routes to take, so don't just take my advice.
Good luck,
Val