Boomers are attractive volunteers, and it's not just the sheer strength of their numbers — 77 million. They are living longer. They are more educated than previous generations. And, especially appealing: They bring well-honed skills and years of real-world work and life experience.

"What we have with the transition of the boomers across the traditional age of retirement is a great opportunity," says Dr. Erwin Tan, who heads the Senior Corps program at the Corporation for National and Community Service, a federal agency in Washington. Senior Corps helps connect older Americans to service jobs.

"The question for us is how can we as a country not afford to mobilize this huge source of human capital to meet the vital needs of our communities," said Tan, a geriatrician. He says nonprofits are retooling to attract more boomers by offering a variety of skills-based opportunities as well as more flexibility, such as nontraditional hours or projects that don't require a trip to the office and can be completed at home.