I'd first like to say that you're lucky that you know so early what you want to do for a living. Definitely take some flying lessons as soon as possible. Your local FBO should be a good introduction. Getting your Private at an early age would be a good stepping stone. I'm sure you would enjoy a part-time job in aviation while you're still in high school--it would be a good introduction and it will look good on your resume.
If you want to be an airline pilot you need to make yourself marketable. Get a college degree. Since you already know what you want to do, I would recommend a University with an intensive flight-training program. Look for "Part 141" schools--they will have set programs and higher standards.
It will cost more that you can imagine, but remember that it is an investment. Also, don't be in too much of a hurry; some regional airlines will hire good pilots without a degree, but you will regret it down the road if you don't get one. Also, you will be at least 21 before you will get hired.