Find second-career work opportunities that are fun, fulfilling and flexible. — Barry Austin/Corbis

Americans are working long past what was once considered retirement age and many are shifting careers as they get older. For some, changing careers is a necessity — they have been downsized or retired but still need income -— while others switch gears to pursue ambitions they put on hold years ago.

"It is a process, discovering what the next act will be for you," career coach Nancy Collamer tells AARP Radio host Mike Cuthbert. "What do you want your life to be like? It's about tapping into your strengths and interests."

In her new book Second-Act Careers: 50+ Ways to Profit From Your Passions During Semi-Retirement, Collamer examines the phenomenon of people jumping career tracks later in life, and says that planning, if possible, is key to a happy second-act career. "You need to first think about the type of life you want to have," she says, "and then build around that."