Hey,
Here's a few things that would be good to consider prior to training:
Do your A levels
Do a try flight
Some nice UN-BIAS advice can be found on BALPA's website. Definitely sign up and learn about some of the realities about the industry today.
Subscribe to Flight International or Airliner to give you some GOOD topical insight into the industry; not just aircraft, but other important aspects, including technology, airport management, growing industries and economics. Showing you have an extended interest in becoming a commercial pilot shows your not a fake and really made the effort to get where you want to be.
Get a class one medical and undergo an aptitude test - these can be the real decider on your future.
And remember not to tie yourself to one career and focus on getting an education - i did that during my A levels and ended up dreaming too much!
good luck!