Hello Jack. Its great that you are in 8th grade and already know what you want to do in the future, huge props for that! Airlines really look for how much flight time and what type of ratings you have. College and GPA may not play a factor at first. I know plenty of pilots that go basic academic thru school and college just to get a college degree and leave plenty of time and money for flying. Don't get me wrong, a good education will always help you in the end, but as a pilot you are not going to need advanced calculus and algebra. I have never heard of an interview that asked what was your GPA. If anything, I may recommend business courses and maybe some psychology classes. As a pilot you will interact with passengers, and know how they act and think can help in situations. Eventually, like anything else that you are going to do every day over and over again, piloting may start to loose its appeal. Advancing higher will require a college degree, and having a business degree will help put you in management. Its always good to have something to fall back on. Remember that airline pilots have to pass a rigorous physical every 6 months. As you get older and your health and family life changes, you want to have that back up.
For now, I would recommend that you find a flight school nearby and start flying. Have your parents help you look for financing. Flying is expensive and you need lots of it. Take out a loan and negotiate with the school. Get your private pilot license and start working on your IFR rating and your CFI. CFI (certified flight instructor), as you start teaching others, you are building time and experience, and getting paid for it. In the same time as you are around an airport, start to network, get to know people and let then get to know you. Good jobs come from who you know. Flight training will give you what you need to be a pilot
Military is another option, but with all these drones and space equipment its getting harder. Most military pilots come from the military academies. If this is something that interests you, start preparing for the SATs, and join the Civil Air Patrol or the Sea Cadets. I believe the Academies will not consider anyone with an SAT score lower that a 1200. There is ROTC and you can also enlist, but those are not always a sure thing.
Hope this helps, and good luck. Keep flying, your hard work will eventually be rewarded.