Michelle Hynds was working at a security job seven years ago when she began to take flight lessons at an airport near Ventura, Calif.

Ms. Hynds, 42, decided to make flying a career instead of a hobby. She gained experience at the controls, got a job piloting a propeller plane for a traffic reporter in Los Angeles and then went to work for a charter jet company. Now, she thinks she can move up to a regional airline, which would put her on a track for a job with one of the big United States carriers.

“It’s the job seeker’s market,” she said. “I need them, for sure, but there’s so many companies that need me.”

Thousands of pilots at the country’s largest carriers are nearing retirement, opening up opportunities for those, like Ms. Hynds, who pay up to $200,000 for the training necessary to advance as an aviator.