Nearly three years ago, I started following the lives of six New Yorkers over 85, one of the fastest-growing age groups in America. As the series went along, the elders focused not on their declining abilities but on things that they could still do and that they found rewarding.

As Ping Wong, 92, said, “I try not to think about bad things. It’s not good for old people to complain.” 

Here was another perspective on getting old. It was also a lesson for those who are not there yet. The message was so counterintuitive that it took a long time to sink in. But finally it did: If you want to be happy, learn to think like an old person.

Fred Jones died of a heart attack in April 2016, just past his 89th birthday. John Sorensen died two months later, refusing food in a nursing home he had never wanted to see. He spent his last days listening to operas and thanking anyone who came near. 

For the others, 2017 was a year of continuities and great changes. 

“I think my life is happier now,” said Helen Moses, 93. “I don’t look at the price when I go shopping. If I like it I buy it. But when I was young if it was too expensive I couldn’t buy it.”

For Ping Wong, who moved to a nursing home near her daughter in southern New Jersey, 2017 was a year of making adjustments.

“At the beginning, of course, I don’t like this place, but gradually I think it’s good for me to stay here, because I meet a lot of honest friends,” she said. “I like the life here much better than young times. Young times we only have time to study and make money. I couldn’t remember when I was young, what we were interested in talking about. Nothing.”

Ruth Willig, 94, took a fall over the summer, when she stood up from a chair and felt her left foot give way. The foot hurt, but “a lot of things hurt,” she said. “If I cry every time it hurts I’d be crying.”

Jonas Mekas, 95, made progress toward a goal that has driven him since the start of the series: raising money to expand Anthology Film Archives, the nonprofit organization and theater he helped start in the 1970s. Mekas also published a book of anecdotes and images this year, “A Dance With Fred Astaire,” named for a Yoko Ono and John Lennon movie in which Mekas and Astaire both make dancing cameos. Another five or six books were almost ready, and a couple of films still needed finishing.

For now, he said, “I’m thinking about resistance. What does it mean, resistance? What kind of resistance do we need today? Technology is now being used, much of it, for negative purposes. So to resist all what is happening negatively in humanity or technology is to develop the — OK, this banal word, spiritual aspect.”

John Leland’s book based on his “85 and Up” series — “Happiness Is a Choice You Make: Lessons From a Year Among the Oldest Old” — will be published on Jan. 23.