While there is no college requirement to be a pilot, most airlines look for some college time and prefer an earned degree. College shows that you are trainable and that you can stick to a challenging curriculum and succeed -- qualities an airline would like to know that you have before it spends a lot of money to train you. There are two major career paths to being hired as an airline pilot: civilian or military. Each has its advantages and disadvantages.
In the civilian career path, you can attend a college that offers a two- or four-year degree (some universities even offer advanced degrees in aviation) along with flight training toward various pilot certificates. Several universities in the United States and Canada offer courses along with flight training so that you graduate with a bachelor's or associate's degree in aviation along with a commercial pilot certificate and multi-engine and instrument ratings. There are also technical schools that offer flight training toward a certificate, often in less time. In both types of programs, you often graduate with an instructor's rating, and you've built up some flight time teaching others.
An alternative to a professional school or college is to get your flight training piecemeal from a local flight school. It will take longer, and the level of instruction might not be as rich, but all commercial certificates are equal in the eyes of the FAA. The agency doesn't care where or how they were earned.
Civilian training costs a lot of money. Basic flying lessons start at about $80 an hour, and you'll need at least 250 hours before you have your commercial rating. It also costs a lot to rent large, complex airplanes for instruction. I like to think of the expense as an investment in a rewarding career that will pay dividends for years to come. Scholarships (full and partial) do exist, but most pilots will end up investing a lot of money in flight training.
In the military, you commit to many years of service after your one year of pilot training (10 years of commitment in the Air Force). You must also meet other requirements, such as college course work, good health and adequate physical ability. There are no guarantees that you'll pass the military flight training on the service's rigid time schedule, or that you'll get to fly a specific airplane. In exchange for these compromises, the military pays you to train, and you get the best training in the equipment that an airline pilot would fly (complex jets).
A military pilot lives a military life, follows orders, risks bodily harm and uses lethal weapons. These aren't things to take lightly, so if you are considering the military (and that is a wide field that includes the Coast Guard), then explore it thoroughly and see if the timing is right for you and your career needs. It is an excellent experience for many people. Some pilots even make the military their career.
After a pilot is certified, he or she will have to get more experience and flight hours before an airline will hire him or her. Because of the military's service commitment, a military pilot will probably get a lot of flying experience before he or she leaves to join an airline. A civilian pilot, or a military pilot who needs more flight hours, may work as a flight instructor, then perhaps move to a charter company. From there, he or she might move to a regional airline and then on to a major airline.