HOW TO BECOME AN AIRLINE PILOT:
(Civilian route)
1. Get your degree. You do not need a degree in aviation, but having a degree in any subject is a requirement to getting hired on at a major airline. The regionals aren't so picky. Many think they must have an aviation degree to have an edge but when or if you are ever furloughed during your career an aviation degree is useless.
2. Get your pilot certificates and ratings via a flying club or school at the local airport, a university aviation program. A newly certificated commercial pilot with instrument and multi-engine ratings usually has about 250 hours. This is not enough for the airlines*. (See note* at bottom) There are also programs like the ATP Career Track that get you certified then have you instruct for them and promise a preferred airline interview (At a cost of about $39K, which is the low end that you should expect to pay to get your licenses & ratings. Other schools are upwards of $80K).
3. Build up flight experience until about 600-1,000 flight hours. Most regional airlines require pilots to have at least that much flight time (their "minimums" or minimum requirements), with 100 of that being in multi-engine aircraft plus Commercial/Multi/Instrument pilot certificate. (An Airline Transport Pilot certificate is not required to be hired.) Common time building jobs are: banner towing, skydive pilot, pipeline patrol, traffic watch or flight instruction (with the additional Certified Flight Instructor rating)
4. Upon reaching the "minimums" begin applying! Hopefully you will get hired. Learn to live on a budget as regional airline pay is not very good. After building up about 2,000-3,000 hours and "paying your dues" at a regional you then qualify for a job with a major carrier.
5. Begin applying all over again with the majors.....
* There are some airline academy programs (Delta Connection Academy, Mesa Airlines Pilot Development, Flight Safety among others) that offer a "quick entry" scheme into the right seat of a regional airline. They are very costly and do not guarantee a job, but an interview only. If you pass their program and the airline interview, you could very well be hired as a First Officer at 300-400 hours
For more stuff you need to know, visit:
http://www.pilotcareer.infohttp://www.jetcareers.com REGARDING THE AIR FORCE (or military):
If you simply want to become airline pilot, do not join the military simply as a means to that end. Do it if you want to serve your country but don't think of it simply as a way to get "free flight training" so you can become an airline pilot.
In all reality, it's not truly "free" and the openings for military aviators are fewer and more competitive than they have ever been. If you somehow manage to even get accepted into the service as a pilot candidate and make it through flight school, you will be committed for a decade or more. You could also get killed in the line of duty.
In years past, the major airlines drew almost exclusively from former military pilots. Former military pilots either dominated the hiring boards or they would recommend their friends who were getting out of the service and looking into airline careers. This big "squadron buddy" network was how the majority of pilots got hired. That is not the case today. For several years now the airlines have been increasingly hiring pilots from a civilian background. According to statistics compiled from Air Inc, about 65?f new hires are civilian. This is partly the result of a smaller pool of military pilots available to the airlines than in decades past and the increase in the number of civilian trained pilots with previous jet and airline experience. Almost all the regionals now fly jets, many that go higher or are more advanced than mainline aircraft. Additionally, most pilots looking to move onto a major carrier will have several times over the amount of flight experience as a military aviator because of their regional job.
BTW- Since you are only 15, I suggest joining the Aviation Explorer Scouts or the Civil Air Patrol. Both will get you into the world of aviation and the cost will be minimal. You may even find reduced cost flight training.
Aviation Exploring is a youth development program centered around aviation careers. Member benefits: orientation flights in military transports, helicopters, gliders, or single-engine general aviation aircraft. Visit Air Force bases, aviation museums, air shows, or FAA facilities. Learn to preflight an aircraft. Take pilot training ground school classes. They also offer scholarships for those on the aviation career track.
http://www.aviationexploring.org/ The Civil Air Patrol offers cadets the chance to take orientation flights in powered and glider aircraft at no cost to them. Paired with an experienced CAP volunteer pilot, cadets help preflight the aircraft, observe takeoff procedures and while aloft actually manipulate the controls and perform basic flight maneuvers. The program also enables cadets to learn about meteorology, navigation and aircraft instrumentation and technology. CAP Cadets fly approximately 16,000 hours in powered aircraft and 7,000 sorties in gliders each year. CAP cadet info-
http://www.cap.gov/visitors/members/cadet_programs/