A Wall Street Journal article earlier this week described a new retirement formula that younger people are using to game out when they have enough savings to start coasting.

The intense focus on building a nest egg is nothing new for many retirees. We asked a few of them to share the lessons they learned from saving and juggling money priorities, and the surprises they encountered along the way. Here is a selection of their stories.

Joseph Kelly | Age 66 | Knoxville, Tenn.

Joseph Kelly's new car is about 11 years old. The one he owned before that was a 1991 Honda Civic. He credits living frugally in all aspects of his life with allowing him to stow away enough savings to retire at age 55.

He formed his retirement-saving habits when he was early in his career as a food scientist. Watching older workers get laid off from his company made him realize the same could happen to him. Kelly invested mainly in stocks and would buy more during market tumult. He later diversified into bonds. His company offered both a pension and 401(k) plan when he worked there.

When Kelly turned 50, he started running calculations on when he could retire. He and his wife, Patricia Kelly, wanted to travel more. If he left at age 55, he could keep his health insurance at the company rate until he turned 65. Kelly set a countdown timer on his work computer until his 55th birthday.

David McNicholas | Age 60 | Broomfield, Colo.

A financial blowup changed David McNicholas's perspective on saving. The IT salesman and consultant had taken on debt to start a company. Then the company went belly up.

He had to liquidate his 401(k) to pay the debt. At 30 years old, McNicholas had a negative net worth. "I realized: Never spend more than you have," he said.

McNicholas said he became "maniacal" about saving and investing, self-directing his investments largely into index funds. "It was just restraint and discipline," he said. "For people that are in their 20s and 30s that are grinding, it's exactly what you're supposed to be doing."

Then, at age 57, a certified financial planner told him he had more than enough saved to retire. He kept working for a few more years, then called it quits earlier this year.

Mike Peterson | Age 67 | Rancho Palos Verdes, Calif.

After retiring at age 61 from his job in emergency medicine, Mike Peterson took on some teaching work, including teaching medical residents personal-finance skills. He tells them about his own mistake of not putting money into retirement savings until he was four years out of residency.

"If I had contributed, I would have an additional half million dollars in my retirement accounts," Peterson said. "I just didn't understand that I needed to do it at that point."

Doctors often enter their professional lives playing catch-up on saving. But Peterson said that spending most of his career working for a county hospital helped him.

He had access to both a pension and defined-contribution plans with employer matching, though it was sometimes tough to maximize saving when he had young children. Today, both factor roughly evenly into his retirement savings.

Nick Greksouk | Age 74 | Alexandria, Va.

It wasn't until Nick Greksouk and his wife were done raising their five children that he was able to max out his retirement savings. When he started his career in the 1980s, concerns about the solvency of Social Security made him fear that no one would be able to retire. Plus, he enjoyed his job as a CPA.

"I never really thought about coasting," he said. "My main goal was to get enough savings, but emphasize the needs of the family first."

But as his children left the house nearly two decades ago, he turned his focus to retirement. Markets went on to have a massive bull run as they recovered from the financial crisis of 2008, helping boost his index-fund investments. Greksouk retired about 21/2 years ago.

Lloyd Vaughan | Age 79 | Dallas

Lloyd Vaughan left his career as a hospital chief financial officer at age 49 and started his own business. The firm helped hospitals collect additional revenue by correcting billing errors.

He grew the company for 21 years, at times forgoing retirement-saving to do so. "I put some in a 401(k), but I wanted to build wealth from the firm," he said. "It was a gamble, but I was very self-confident."

Sure enough, he sold the company to a private-equity firm at age 70, which funded his retirement. He knows his situation is unique. He has since mentored people hoping to start small businesses, and he has suggested to some that they not quit their day jobs.