I can’t seem to resist the temptation to re-hash some of what’s been said already and add some of my own thoughts:
Two main options to get there are militay and civilian.
Going the military route, your best best is to go Air Force, but the commitment time is huge, and even after 11 years in the AF, you’re by no means guaranteed to walk into a major airline. I believe the Navy’s commitment is a year or two less than AF, but you are less likely to fly an aircraft that will translate well into flying airline jets (half of Navy pilots fly helicopters). Army guys very rarely get to fly the kind of aircraft that will get them airline jobs.
Going civilian is riskier and more expensive, but might be a little quicker. There are several schools that specialize int raining pilots. (Embry-Riddle is probably the best known, but there are others). This route will certainly require that you spend years, perhaps decades, working some not very glamorous aviation jobs - teaching lawyers to fly their new airplanes, flying puddle jumpers and loading the passengers luggage yourself, etc.
Some other things to consider:
Until you’re on track at a major where the pay is remarkable (100-200K depending on equipment and seniority) you’ll be making very little money. in the 20’s and 30’s is not uncommon even at some of the bigger regionals.
The industry isn’t as exciting as it used to be - much of the flying is done with the autopilot. “Excitement” can be a bad thing from a marketing point of view – people want their air travel safe and stodgy. Cheaper air travel for the masses has turned flying into a simple means of travel and less of an experience than it used to be. It’s hard to believe that people actually used to dress up if they were getting on an airplane! (bottom line: If you’re imagining “catch me if you can” those days are long gone.) There are certainly plenty of “exciting” flying jobs in the military, and a few in the civilian world – fire fighting, for example. Lots of helo jobs have that excitement factor (law enforcement, life flight) but also don’t pay very well (30’s - 40’s).
By the time you’d be ready to break into the industry 10-15 years from now, things may have changed a fair amount on the pay front as well. The smaller start up airlines are chipping away at the big guys, and all of the big guys are looking at their pilots to make pay concessions to help out.
All that said, SOMEONE out there is getting paid $240K a year to flying 747s into Heathrow, and that wouldn’t suck.