Right now, as is already covered, you need to be 23 by Aug 1, 2013 and thereafter with 1500 hours to be hired by an airline.
You will have to start off at a regional carrier, small corporate flight department, or a charter operation prior to making the jump to a major carrier. Even then, some major carriers (southwest, to be specific) require a certain number of hours as a CAPTAIN prior to them accepting your application. If you add up time building, getting hired at a regional airline, and upgrading to captain and getting you 1000 PIC of a jet, you are looking at a large amount of time measured in years.
My advice to you is to enjoy the road ahead and have fun time building. I instructed for over 2 years and enjoyed it, and now am living the regional life flying the CRJ for a major regional carrier here in the US. While not glorious, i love my job, and while there are plenty of things that could be better, eventually some day i'll make the move to a larger carrier with a etter quality of life.
And a very, very good piece of advice: make sure you never tell someone in the industry you hope to fly for southwest, or any other major carrier coming out of college. Chances are you'll be telling that to a check airman who has 7000 total time, with 4000 PIC in a jet and is still waiting for an interview there. I mean this with all due respect...When i head to work, i of course hope one day i am at a major, but realize people have worked for years to get where they are and sometimes the ignorance of a aviation college graduate thinking he'll get things handed to him....just isnt the case. youll thank me later. Take any unexpected career advances as luck, and be thankful youre healthy enough to qualify for a medical and watch sunset at cruise
keeps me happy!