If you are asking about being a pilot for even a regional carrier, I would say that your chances are nil. There are any number of young, well-trained, highly qualified pilots coming out of the military all the time. The regionals (and the majors when hiring) snap them up. By the time you got sufficiently trained and rated, you would probably be close to 60 and the mandatory retirement age for pilots is 65.
Most of the "cargo" airlines--like FedEx and UPS--hire pilots furloughed from the majors when they can. They can get people already trained on specific a/c types.
If you are just talking about working for an airline--gate agent, flight attendant, etc--chances are better. I am 64 and started flying as a flight attendant at the age of 55. However, as far as I know, none of the major airlines is hiring right now. At AA, we are laying off people as capacity continues to be cut.
I'm not saying becoming a pilot is impossible, but I would make sure you have a Plan B if you want to pursue flying as Plan A.
