But he came to see that his research also revealed a brighter side. Despite the challenges of old age, people reported being happier as they hit age 65 and beyond.

Thus began his 10-year project interviewing more than 1,200 Americans between the ages of 70 and 108, with an average age of 77. These were elders who'd lived through the Great Depression and World War II, and even some who'd survived the 1918 Spanish flu pandemic.

If they could not only survive but thrive through these difficult times, surely they had lessons for the rest of us, figured Pillemer, who's also a professor of gerontology in medicine at Weill Cornell Medicine, the biomedical research unit and medical school of Cornell University.

What seniors can tell us about living well

Pillemer wasn't interested in the broad, sweeping advice — what he calls Yoda-type wisdom — of seniors. He wanted practical, everyday advice on living based on their experiences enduring those major historical events.

The result of that work is his 2011 book 30 Lessons for Living: Tried and True Advice from the Wisest Americans, which covers topics from love and marriage to work and career to avoiding regrets. It was named a "Best Self-Help Book of 2011" by Library Journal.

Pillemer also created the Cornell Legacy Project where he has collected the advice from seniors and their solutions to major problems into "lessons" arranged by category.

It was important for Pillemer to gather that wisdom from that particular group of seniors before it was too late, he says, noting that humans have always looked to their elders for advice — until recently.

"It's weird. Only in the past 100 years have people asked anyone other than old people for advice," he says. "Our society is the most age-segregated it's ever been. Young people have almost no regular contact with older people unless they are a member of the family. I wanted to encourage people to see their elders as sources of wisdom."

Pillemer gained a few life-changing lessons himself. "The advice that worry wastes your life did profoundly affect me," he says, calling himself a Woody Allen–type worrier, more focused on the future than the day at hand.

"And they make you aware that you have a limited time horizon," he says.

Another lesson that Pillemer admits sounds cliché: "Happiness is a choice and not a condition; you have to exercise your will to be happy. Learn to be happy in spite of things."

Pillemer hopes to inspire others to interview their elders. "It's a powerful experience for older people. Often they're asked for their history, their stories. But I find it's powerful to ask, ‘What are the most important lessons you have learned over the course of your life?'"

The answers from these wise "life experts" are invaluable to all of us still struggling to figure out how to best live our own life.

When thinking about the lessons you have learned throughout your life, think about your loved ones and what needs to be considered when you pass. To help cover final expenses or things that may come up after you pass, consider Guaranteed Whole Life Insurance through United of Omaha Life Insurance Company, a Mutual of Omaha company. This policy is available for people ages 45-85 (NY, 50-75) and is there to help give your loved ones some peace of mind and help cover any final expenses.