Some seniors are content to retire. Some will never do so.

Beth Bergmans enjoyed working as a project manager at an online university based in Minnesota. “We provide opportunities for people to grow in life—that gave me a certain satisfaction,” she said. “And the people I work with are amazing.”

Ms. Bergmans, 63, had planned to stay in her job for two years, until she qualified for Medicare. But something had subtly changed in recent months. The fast-paced pace of her work made it harder for her to recall details of recent meetings, to find words and to filter out distractions. She took compact breaks at her desk to recharge.

“You find ways to adapt,” she said. “You exploit Post-it notes and whiteboards and spend more time preparing before meetings.” No one complained or even seemed to notice, but Ms. Bergmans worried.

“People don’t really talk about it, the fear that you’re starting to slide professionally,” she said. “The last thing I want is to crash and burn at the end because I didn’t recognize that it was time to stop.”

A few weeks ago, Ms Bergmans told her manager that she would retire at the end of the year.

Sometimes this happens: people who are committed to their career and proud of it, intending to continue it beyond the typical retirement age, encounter internal or external difficulties and leave, even if no one is telling them to give up or retire.

And sometimes, even if many People encourage them to do so, but they just say no.

President Biden (who is 81 and has not been deterred by doubts about his age and abilities) and former President Donald J. Trump (who is 78 and has not been deterred by criminal convictions and other legal challenges) are the latest embodiments of this response, but they are certainly not the first.

Consider Dianne Feinstein, a six-term senator from California who has faced questions about her competence as she grows increasingly infirm and disoriented. She has agreed not to seek reelection after her term ends in 2025 but has refused to resign.

When she died in office last fall, she was the oldest member of the Senate, at age 90. (Senator Strom Thurmond of South Carolina, who resisted similar entreaties, retired at age 100 and died shortly thereafter.)

Consider Sumner Redstone, who has maintained leadership of his $40 billion media empire, including Viacom and CBS, despite pressure from investors and analysts. When asked by a reporter about his succession, he replied, “I have no intention of dying.”

After a lawsuit that portrayed him as mentally disabled, Mr. Redstone resigned from CBS at age 92 and from Viacom at age 93, sparking legal battles for control of the companies. He died in 2020 at age 97.

“People who have more power, status and control over their jobs are much less likely than others to decide to retire voluntarily,” said Teresa Ghilarducci, an economist at the Recent School for Social Research and a longtime retirement researcher.

“People with authority in the workplace actually experience less stress,” she added. “Having an older boss is bad for your health, but being the boss is good for your health.”

Only a fraction of older Americans fall into this category, where good health allows for a longer career and financial security makes continued work unnecessary.

Dr. Ghilarducci analysis data from the National Health and Retirement Survey shows that only a third of working people aged 62 to 70 can afford to retire but do not want to. Most people who are still employed at this age work because of financial need.

In 2022, nearly 40 percent of U.S. households were at risk unable to maintain their standard of living in retirement, according to data from the Center for Retirement Research at Boston College.

“It’s a sporadic bird,” said Lisa Berkman, an epidemiologist at Harvard TH Chan School of Public Health who has written about longer careers. “Very few people have the luxury of working because they love their job and want to continue working.”

She added that people who work solely because they want to be wealthy and well-educated have malleable working conditions and jobs that are not physically demanding.

Most older workers are more like Rob Belgeri, a 70-year-old union representative in Redding, Calif. He had planned to retire around 65, but after having coronary artery bypass surgery at age 54, he found that his demanding job was more tiring, “like being stuck in neutral, not being able to get into gear.”

He said he would wake up at night, afraid he had missed an significant deadline, even though he never did, and his superiors had no complaints. Despite that, Mr. Belgeri stayed on for another six years, until he was finally able to draw a union pension at age 60, with relief.

Or they’re like Myrna Cozen, a 74-year-old epidemiologist in El Cerrito, California, who was abruptly laid off in May along with dozens of her coworkers. She wants to keep working, but “I’ve applied 30 times and haven’t gotten a single positive response,” she said. “Just like we do in politics, we assume people based on age.”

Why not hand over the reins when you have doubts—yours or those of others—about continuing? After all, retirement can be appealing. Most retirees said they feel “free” (59 percent) and “relaxed” (72 percent) in AARP survey. An international meta-analysis found that retirement is associated with reduced risk of depression.

Popular culture tends to glorify this stage of life: notice all those older couples dancing on beaches and cruise ships in TV commercials.

However, “the reality is that retirement can be a very complex time,” said Teresa Amabile, a psychologist at Harvard Business School and co-author of the upcoming book “Retiring: Creating a Life That Works for You.”

After a decade of research on retirement paths for professionals and managersHer team found that breaking away from work can be complex, and this phase often lasts two to three years for retirees to get used to their up-to-date lifestyle.

The end of a career means “losing being an employee, a member of an organization or a profession,” said Dr. Amabile, who retired this month at the age of 74. It is “losing being needed, counted on, respected, perhaps powerful, if you were the head of a enormous corporation — or the president of the United States.”

Dr Ghilarducci stressed that forced resignations or retirements, such as those resulting from scandal, a health crisis, dismissal or election defeat, are particularly worrying.

“You’re more likely to be depressed and anxious,” Dr. Ghilarducci said. “Being forced to leave is one of the worst things that can happen to an older person.”

The researchers identified a sequence of developmental tasks, or phases, that older workers go through to find satisfaction in life after retirement. When retirement is involuntary, “the tasks associated with retirement short-circuit,” Dr. Amabile said.

“One never has a chance to make a conscious decision. There is no sense of career closure, no sense of agency and control.”

Dr. Amabile says the difference between people who step aside and those who don’t, though it’s not a well-researched topic, may come down to self-awareness.

When Benedict XVI, then 85, became the first pope in six centuries to resign from office, his power had so diminished that “I had to recognize my inability to properly fulfill the ministry entrusted to me,” he said.

Philip Roth announced at the age of 79 that he had stopped writing fiction because, he said, “I know I’m not going to write as well as I used to.”

On the other hand, some former admirers are still livid at Justice Ruth Bader Ginsburg, who beat cancer multiple times and remained on the Supreme Court until her death at age 87. She ignored calls to resign before former President Barack Obama left office, not because of concerns about her competence but so he could nominate her successor.

So far, no one seems to be upset about the long career of Warren Buffett, 93, the Berkshire Hathaway chief executive. Neither is Mick Jagger, 80, or Mavis Staples, 85, both on tour this summer. Representative Nancy Pelosi, D-Calif., has found a middle ground: She has resigned as speaker of the House but remains in Congress at age 84 and will be on the ballot in November.

Beth Bergmans’ professional life was much shorter, but she considers herself “one of the lucky ones,” she said. “I have a choice.” In January, one of her first acts after retiring will be to stop multitasking while listening to audiobooks.

At her home in Nowthen, Minnesota, she said, “I’ll sit in a chair with a real book in my hand and read the words on the page.”

Teddy Rosenbluth contributed to the research.