Steve Lopez knows he is running out of time.

Lopez, a Los Angeles Times columnist and four-time Pulitzer Prize finalist, isn't collapsing into the grave just yet, but he is 69, with two artificial knees and a pacemaker.

"Although this is a scary thought, when you get to where I am, statistically speaking, you're in the last quarter of your life and most of it is behind you," he said. 

But there are still so many bullets on his to-do list.

He could retire and start crossing some off, but he is hesitant. "Being a columnist I've had a quasi-public life," he said. "After that, who am I going to be?" 

He wanted to find out before the health problems that affected his parents interfered. 

"I mentioned it to everybody who I considered a peer age-wise, and they were all having the same conversations with themselves and others about when is the right time to go." 

To discover why some people retire and others don't, and what makes retirement fulfilling, Lopez talked to dozens of older adults for his new book "Independence Day: What I Learned About Retirement from Some Who've Done It and Some Who Never Will." 

He interviewed a priest who said he was going to retire "in the graveyard" and a winemaker who said they'd retire "in the vineyard."

He interviewed a man who retired but soon after found himself as the cashier at a checkout counter, working to make ends meet.

He interviewed Mel Brooks and Norman Lear, both of whom are in their 90s and working. 

Financially, there is an amount of money experts say you can retire comfortably on, and Lopez said he doesn't mean to diminish the importance of figuring that out. "People who had money are reveling in their retirement," he said.

But mentally, how do you know when it is the right time to walk away? 

"There are a lot of books on the financial skepticism of retirement," he said. "What about the spiritual side?"

CNBC Make It chatted with Lopez about how to face retirement and find purpose after working. The interview was edited for clarity and brevity.

'Be ready to adapt'

Aditi Shrikant, CNBC Make It: You interviewed dozens of people on retirement. What lessons or pieces of advice stuck with you most?

Lopez: The most important lesson that I took from my experience is not to be cavalier about walking away. You need to have a real sense of how you might matter, and I think there is a human instinct to be relevant. And whether you matter to your cat or your dog or the people at the nonprofit, you need to construct a life that gets you out of bed in the morning.

The best advice I got was to be ready to adapt and expect the unexpected.

There was one guy who retired and wanted to travel the world then found his daughter and his granddaughter needed help. He said he knows no one else who had the retirement they had planned out.

You'll do yourself a favor in anticipating that this phase of your life will be all about change and some of it will be good and some of it will be difficult.

There are those who can wing it and there are those who retire to the remote control and catch up on old movies. But we are running out of time, and it's important to be smart about who you are and fit yourself into the time you have remaining.

And another piece of advice from a rabbi who retired then decided to go back to work is to try to sample what you think will take up your time in retirement to make sure the thing you idealize is worth your time. 

Shrikant: Have you thought about this advice while planning your own retirement? 

Lopez: Well, the pandemic shut down my office. Having the office closed meant working from home far more than I ever have in my life, and my wife is a freelance writer who works at home.

We were sharing an office for the first time in our lives and we don't live in a sprawling mansion so there was a lot of bumping into each other. 

This pandemic was serving us a preview of what our retirement would be when I'm spending more time at home. My wife told me, "If this is the preview, I don't want to see the movie." 

You have to manage and adjust those types of relationships. She is working and doesn't need me sitting around asking what we are going to do next. 

I'm still working three-fourths of the time, but I'm working mostly from home. We are still adjusting to that, and I'm finding that I'm loving playing the guitar and I've gotten a lot better in a year.

I'm not doing so well on [learning] a language, and I'd like to do much more travel. That's been more difficult because of the pandemic restrictions.

I'm hoping that next year I go half the time [to work], and then I begin to slowly step away. 

'Retirement can and should be full of surprises'

Shrikant: How did relationships play into the lives of the retirees you talked to? 

Lopez: I interviewed people who are lonely and who feel isolated and depressed. I got people who wished they had even more time to do all the things they did in retirement.

Of course it's a blow to anybody to lose a spouse in retirement, and there are these tragic cases of people who retire to spend time with a spouse and discover a health problem gets in the way.

This woman, Nancy, in Florida, did not anticipate her husband would die as early as he did. She didn't know she would fall in love again, and she did not know she would lose the second man in her life. Then when I was talking to her, the phone rang and it was her new boyfriend.

Retirement can and should be full of surprises, and you've got to be able to roll with them. 

Shrikant: Did you find that men and women handle retirement differently? 

Lopez: My sense is that women are much better at this than men. Men are more impulsive and not as bright as women.

There was a professor at Brown [University] who was telling me he sees this with men. He teaches geriatrics. He talked about how women throughout their lives are multitasking much more than men, and because of it they are better trained to handle time.

They are more inclined to figure things out, to act with forethought, and make reasoned decisions about things.

Women are stronger than men. We are too fickle and not cut out for retirement, and I saw that in the women I interviewed for this book. 

Shrikant: You interviewed some pretty high-profile people. What did Norman Lear have to say? 

Lopez: I was interested in Mel Brooks and Norman Lear not only because they are celebrities and Hollywood legends but because they are working in their 90s. 

[Lear] said life is about that little space between what's over and what's next.

What happened yesterday is over. Yes, he created "All in the Family" and "The Jeffersons" and produced movies and has done like 60 years of breakthrough television, but it's over and he's not sure what's next.

Shrikant: And what about Mel Brooks? 

Lopez: Mel Brooks said, "I understand you want to live in Spain and search for your grandparents' home towns, but how long do you think you'll be there before you find a story in it?"

He asked me how long I will be living in my new home in Barcelona, learning how to cook tapas, until I think, Hey, there's a good story in this; let me call my friends at the LA Times.

Or, maybe, it's pitching a podcast. In my case I've also tinkered with this idea that as I age, aging can become my specialty.

I could write a column about aging in California. I could call it 'The Golden State.'

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