A couple of years ago, my relationship with work started shifting. For 25 years as a writer and editor, I had run the rapids of Washington’s river of ambition, always seeking the next challenge, the next triumph. If I wasn’t under a deadline or bowing to a self-imposed task list, I didn’t feel whole. I assumed that the ambient unease this brought was what experts call “good stress.”

But then I started finding myself bobbing in an unfamiliar eddy: contentment with my station in life. I was a healthy 50-year-old with a wife, two kids in elementary school, aging but remarkably spry parents and a deep community of friends. It hit me: Perhaps I should enjoy this setup while it lasts.

I began noticing changes, most of which seemed to be happening without purpose or intention on my part. I became more selective in pursuing freelance writing gigs and less anxious about how they would turn out (like many creative types, self-doubt has been a loyal wingman throughout my career). I started shrugging instead of stressing if my kids were late for school, and I began engaging wholly with my family after work instead of opening a computer to peck distractedly at a lingering task. The work, the obligations, the annoyances of daily life persisted, but — lo and behold — they didn’t gnaw at me like they once had.

Turns out a host of studies had predicted this shift to a T — or, more precisely, to a U, the shape of the average American adulthood happiness curve: In general, we tend to start our grown-up years feeling pretty good, experience a steady drop in self-perceived well-being until around age 50, then rebound until hitting peak happiness somewhere around age 65 to 72. The curve is not universal — data from economically struggling countries, for example, don’t show the happiness rebound. But a 2012 study of 508 chimpanzees and orangutans found that they, too, experience the up-down-up pattern.

I wondered whether my newfound contentedness signaled an irreversible slide toward the sunset of my career. (If so, will I care?) And why does it happen? I turned to some experts for their insights.

“This is about realizing that we’re going to die one day and being more selective in who we spend time with [and] fully accepting that we’ll never achieve many things,” says Arthur Stone, professor of psychology, economics, and health policy and management at the University of Southern California. He adds that these realizations tend to leave people with smaller but more enriching social circles, a predilection toward happiness over hassle and a higher likelihood of general contentment.

Far from signaling the death of ambition, however, the calm we gain with age can make future achievement more possible, according to psychologist Ellen Langer. Our newfound equilibrium stems from experience and knowing that most things will turn out okay, says the Harvard University professor and author of “Mindfulness.”

“I was recently playing tennis against two younger boys who lacked wisdom of the game,” she says. “They hit better than me and were faster but, as an older person, I have a sense of where the ball is going to go so I don’t have to race all over the place,” says Langer, who is 72. “Wisdom changes the game.”

She adds that it’s often perfectly acceptable for older workers to intentionally lower their productivity. “When I was younger, I felt each journal article I published would make a big difference. Now I realize it doesn’t matter. If I write fewer now, it’s not because I don’t care; it’s because my values have changed.” Langer acknowledges that publishing was important earlier in her career, and she doesn’t regret the time or effort she spent pursuing it.

Sonja Lyubomirsky, a psychology professor at the University of California at Riverside, and author of “The How of Happiness,” doesn’t believe our 50s bring a natural drop in ambition. “That’s the peak of your career. I remember dreading turning 50, and a friend said to me, ‘Sonja, 50 is when you own it! People are running the world in their 50s.’ ”

Um, other people, maybe, but point taken. Perhaps sensing my sudden drop in hedonic well-being, Lyubomirsky quickly adds, “But if you’re slowing down at work and feel good about it, that’s great. You’re making the decisions that make you happy.”

She echoes Langer’s point about clarity and shedding anxieties that almost always do more harm than good. “My younger colleagues are so anxious all the time, and that gets in the way of their work and their happiness,” Lyubomirsky says.

I ask her why people get better at shedding those anxieties as they age. For example, I say, I can go out and enjoy a 45-minute run at lunchtime even though I know I have a mountain of work waiting for me, something I couldn’t achieve a decade ago.

It’s partly physiological, Lyubomirsky says, citing the findings of a 2006 study published in the Journal of Neuroscience (titled “The Mellow Years?”), in which researchers conducted brain imaging on 242 healthy individuals. The scans showed that younger brains were more attuned to fear and less to happiness, and the reverse was true in older subjects. Basically, as we age, we suppress reactions to negative stimulation — particularly threats — while letting positive responses flow without restraint. As Lyubomirsky puts it: “Positive emotions can neutralize negative ones. It’s hard to be bitter and angry at the same time you’re happy.”

Langer offers another example of how the happiness continuum can liberate us, one she hopes will help show younger folks that their elders aren’t necessarily losing it, and in fact are much further along in getting it. “When you’re a young woman wearing pantyhose and they rip, you immediately worry about being negatively evaluated. As you get older, you realize that the people who care about you aren’t going to stop caring because of your pantyhose, and that anyone who is going to judge you doesn’t matter.”

It’s not a situation I’m familiar with, but I understand what she’s getting at. And after talking with Langer, Stone and Lyubomirsky, I’ve concluded that my recent ascent toward Zen doesn’t mean my career’s over. In fact, I think it means something better. In my 50s and beyond, I can be happier in my work — and in everything else.