I would like to pass you the information I was given when I decided age 14 that I wanted to fly for a living. It went something along the lines of do well at school finish your GCSE's and A levels. This will give you a good foundation in life if further down the line you decide, or it is decided for you, that the airline career is not right for you.
All of the Sponsorship schemes I looked at requested the minimums of 5 GCSE's grade C or above including English and Maths, 2 A levels and a minimum age of 18.
I completed my A level course in the knowledge that I wanted to commence a full time ATPL course and not attend University. I still completed the UCAS application procedure and had a place on hold on my chosen course whilst I was completing my ATPL. My best advice is before you set your heart on the Airlines and close the doors on your other career options get a Class 1 medical. This at least proves you have the medical requirements to fly commercially before you commit yourself financially to a course.
I hope this information is helpful to you. This is simply advice from my own experiences. I am now 21 with a frozen ATPL so it wasn't too long ago that I was asking similar questions to seek the knowledge and expertise of my peers. Just remember, a lot of people will have a lot of advice for you, but at the end of the day it is your life and you must make the decisions that you feel are right for you.
I wish you the best of luck and hope you have a succesful career in whatever field you choose.
