Meet a 71-year-old who retired as a radiologist and professor, and now runs a banana-skewer business: ‘I never want to retire. Why would you do that?’

At 71, Richard Brown feels as if he’s a college student all over again.

A nuclear medicine physician turned professor, Brown formally retired in 2020—only to take another job in university leadership the following week and join a venture-backed health care startup. Now, he’s reinventing himself once again, this time as a product entrepreneur—and it has him more excited than ever.

“My hobbies tend to be learning something new,” Brown told Fortune in a recent interview.

“I think I never want to retire,” he added. “Why would you do that? You spent all this time learning something—and things get easier for you when you get older in some ways because you’re a little bit wiser.”

His latest experiment is Poka Snack, a skewer-like product designed to make it easier to freeze and eat fruit, particularly bananas. Earlier this year, Brown launched it on Kickstarter, where it has raised more than 90% of its initial $4,000 goal, and he’s already amassed more than 14,000 TikTok followers.

But for Brown, the venture is more than a frozen skewer business. It’s another opportunity to step outside his comfort zone, learn something unfamiliar, and find the energy that comes with starting over.

“It’s almost like being in college again,” Brown said. “You have that adrenaline flowing. You want to accomplish something.”

Don’t be afraid to ‘look stupid’ and take risks, Brown says

Brown graduated from the University of Michigan’s medical school in 1980 and spent the next two decades in private practice. In 2004, he returned to his alma mater as a professor, while also serving as director of clinical nuclear medicine and molecular imaging in the university’s division of nuclear medicine. He retired from Michigan in 2020.

By then, Brown had spent decades building a career; he could have stepped away and looked back on the patients he treated, the students he taught, and the hefty salary that came with it. Instead, the following Monday he started a new job.

Brown became vice chair of clinical operations at the University of Utah School of Medicine’s department of radiology, a role he held for three years before joining Covera Health, a venture-backed health-tech startup. Today, he serves as the company’s chief health strategy officer.

Still working years after the typical retirement age, constant change and sense of growth is what keeps Brown engaged. Early in a career, he said, much of the work is about learning; eventually, as the job becomes familiar, it can become easier to stop pushing yourself into unfamiliar territory.

“When something becomes routine, you probably have stopped growing,” he said.

That philosophy has shaped Brown’s relationship with entrepreneurship. During the dot-com boom—while still practicing medicine—he launched several internet ventures, including websites that sold college textbooks and hotel rooms around the world. He also created an educational website for cancer patients and their families. While the era’s bust eventually brought most of those ventures to an end, Brown said the experience taught him not to let the fear of failure—or looking foolish—get in the way.

“I think the problem with most people is they’re afraid to look stupid,” Brown said. “If you think that something should be done, just do it. Don’t worry about what other people think, because you may be wrong, but you also may be right. And if you’re right, do you really want to miss that opportunity?”

He’s continued to embrace that mindset with Poka Snack, which was inspired by the fact that while he liked eating frozen bananas, existing products were difficult to insert, sometimes broke and could leave splinters in the fruit.

“I wanted something better,” Brown said. “When I couldn’t find what I was looking for, I decided to see if I could create it myself.”

After testing roughly 40 prototypes, Brown settled on the final design, featuring patent-pending semi-helical geometry. He’s now working with a U.S. manufacturer on production while finalizing the packaging.

How a baby boomer used AI to become a ‘solopreneur’

Brown’s latest venture has also given him a crash course in something else: using AI to build a business largely on his own.

He’s used the technology throughout the entire Poka Snack development process, from product concept and design to branding, creative work, marketing, his business plan, and the launch. Without it, he said, becoming a “solopreneur” would not have been possible.

But the experience has also reinforced a lesson Brown has learned throughout his career: Instead of worrying about finding the perfect career path, pay attention to what genuinely interests you.

“People are always asking: ‘What should I go into?’ and that’s the wrong question,” Brown said. “The question is: ‘What are you excited about?'”

It’s a simple philosophy, but one Brown has spent his career putting into practice: Never stop learning or experimenting—and don’t be afraid to start over.

This story was originally featured on Fortune.com