Katharine Esty, an 86-year-old psychologist, admits she fell into "a funk" when she was about to turn 80 in 2014.
"I was kind of a little depressed," Esty tells CNBC Make It.
At the time, Esty, who in her 70s had no real health issues, was experiencing changes in her body. Suddenly, she was no longer able to do one of her favorite mountain hikes in Concord, Massachusetts, where she lives at a retirement community.
"I couldn't make it to the top," says Esty, who is a widow, a mother of four and a grandmother of 10.
But instead of just feeling down about entering a new decade, Esty, a practicing psychotherapist and social psychologist, decided to interview people in their 80s to find out what life was really like for them.
She was surprised at what she discovered.
"Most people don't know that the aging brain is kinder than a younger brain, so people in their 80s and above are happier than others," says Esty.
In interviewing 128 octogenarians over three years, Esty found that most 80-year-olds are thriving. While "only a handful" of Esty's interviewees were unhappy (some of those living in nursing homes), most of them made peace even if they had pain and disease, she says.
It's not all "doom and gloom" like people make it out to be, Esty says.
So Esty turned her research into a book. Last year, at 85, Esty published her fourth book, "EightySomethings: A Practical Guide to Letting Go, Aging Well, and Finding Unexpected Happiness."
"The stereotypes that people have in their minds about old age are just completely wrong," she says. "The array of what people are doing in their 80s is stunning. Many people are pain-free and living full lives and traveling," she says.
Here's why Esty says most people become happier in the 80s, and what you can learn from it.
In her research, Esty found that a lot of happy 80-year-olds were still working in some capacity.
Some of her interviewees had actually kept their jobs part-time, while others volunteered in their communities in various ways, whether through a church organization or as an activist.
"They had a purpose," she says. "They were participating in the world, and the world had meaning to them."
Esty herself ran a local consultancy until she was 72, and then rather than retire, she went back to psychotherapy work and has been doing it ever since.
Purpose, she says, is what she found helps older people keep going.
Esty found that most 80-year-olds experience less anger, worry and stress than they did in past decades.
Through time and experience, people in their 80s have already experienced loss and other difficult situations and learned to cope better than other age groups.
And though some wished they had divorced earlier or changed jobs or done something else differently, for the most part, they had no regrets because they had made "peace" with their decisions.
Even during Covid-19, Esty says that older people are less stressed and panicky than other age groups because they are already living with idea that death may soon be a reality.
"All of us have been told all of our adult life that you should be living in the moment," says Esty. "But the people that are older are more apt to do it because the future is short."
Esty says most of her interviewees were focused on the present and weren't thinking about future events.
"Nobody was saying, well, in three years, I want to do this or in five years, I'll do that or even two years," Esty says.