Where are the human beings we need to do things only humans can do? That was the founding question, and challenge, behind establishment of Encore.org (formerly Civic Ventures) 15 years ago. After years studying mentoring programs for kids and accumulating evidence that caring adults make an enormous difference in kids' lives, I wondered why so many young people—particularly low-income children of color—were languishing on waiting lists for programs like Big Brothers Big Sisters, oftentimes for years.

The reason seemed to rest on a paradox. These programs, for all their virtues, primarily recruited the busiest people in society—individuals in the first half of adulthood who barely had enough time to spend with their own kids, much less 10-12 hours a month (the magic number it takes for impact) with another's child.

Meanwhile, when it came to harnessing human capital for social impact, and helping young people in particular, programs often overlooked the fastest-growing segment of society—people over 60 years old.

We created Encore.org to help connect the untapped resources older people can provide with critical unmet needs in the social sector.

Our first major undertaking was expanding Experience Corps, a service program that deployed adults beyond midlife to work one-on-one with low-income, inner-city children, mostly in grades K-3. We hoped to catalyze an overhaul of the longstanding, federally funded Senior Corps programs. But roadblocks to that route led us to change course and eventually team up with AARP, which now runs the program. Research studies conducted at Johns Hopkins and Washington University show compelling evidence of effectiveness in improving reading scores. The program is embarking on a significant expansion with plans for a 10-fold increase in tutors to 20,000, allowing it to serve roughly 300,000 students per year.

But even when Experience Corps reaches that goal, harnessing the potential human capital windfall presented by the age wave will require additional solutions to achieve transformative scale.

Already 10,000 people a day in the United States turn 65. By 2030, when all members of the Baby Boom generation have reached that age, fully 18 percent of the nation will be at least that 65. At Encore.org, we're convinced that this population constitutes something entirely new: They are the first denizens of a nascent stage of life that has no name, no clear role in society, and few coherent institutions or policies—yet vast possibilities.

One of the brightest spots is a rapidly growing movement among individuals of a certain age, unwilling to wait for society to invite their contributions; they are forging ahead, working to make a difference, and actively redefining this period of life in ways that hold great potential for themselves and society.

Already, nine million of these individuals have moved into "encore careers"—second acts at the intersection of social impact, personal meaning, and continued income. Some 31 million more say they are determined to do the same. I believe these individuals are poised to reset the social and cultural norm for a successful later life—like the similarly sized vanguard a half a century ago that redefined retirement by moving to recreation-oriented communities such as Leisure World and Sun City, embodying the "golden years" ideal.

In driving a new norm for the years beyond midlife, we're banking on these encore pioneers, and investing in a pair of approaches.

First, we are elevating the encore career phenomenon by sharing stories from the nine million people already in their encore. Among other things, we created the Purpose Prize, an annual $100,000 award that honors social innovators over 60. After a decade, we are approaching 500 total winners and fellows from some 10,000 nominations spanning the socio-economic spectrum. This storytelling work aims to inspire others and construct a new narrative about the arc of longer lives.

Second, we are helping the estimated 31 million people who say they want to lead lives infused with social purpose move beyond the "do-it-yourself" improvisation that so many face today. We aim to devise new pathways to purpose that involve system-level change. Our Encore Fellowships initiative is one such pathway, offering a stipended, one-year fellowship to people interested in parlaying their midlife experience into impact in areas such as education, youth services, health access, and poverty alleviation.

The program has grown quickly to 250 fellows a year, and corporate HR departments are already using it as a model to support creative transitional programs for retiring employees. For example, Intel committed to covering the stipend and health benefits for every retirement-eligible company employee in the United States placed in one of these fellowships. Imagine the potential for scale in making Encore Fellowships and other transition approaches part of the traditional retirement assistance companies offer.

Taken together, the nine million people already pursuing encore careers and the 31 million encore aspirants constitute an extraordinary repository of human beings prepared to do those things only people can do. Our experience suggests that these encores tend to last a decade in duration, so those already engaged or headed down the encore path amount to approximately 400 million years of human capital.

In resetting the norm for the second half of life, the encore movement holds the potential to create a new default position—not just for Baby Boomers, but for their children and their childrens' children. Half of the young people born in the developed world since 2000 will likely see their 100th birthday. Let's hope that they can look forward to lives that still matter in their 60s, 70s, and beyond. That's a transformation that could last for generations to come.

Marc Freedman is founder and CEO of Encore.org (formerly Civic Ventures). He is the recipient of The Skoll Award in Social Entrepreneurship and an Ashoka Senior Fellowship. Fast Company magazine selected him three years in a row as one of the nation's leading social entrepreneurs. He is also author of The Big Shift: Navigating the New Stage Beyond Midlife.