Most baby boomer entrepreneurs are used to working around the clock and aren’t looking forward to retiring, according to a new study by Northwestern University's Family Business Program.

When they do retire, many would prefer to keep their business in the family, the study found.

In a series of interviews with 10 CEOs in manufacturing, commercial services, real estate and retail, many described themselves as consumed by their jobs, devoted to their businesses and reluctant to retire. Despite their advancing age, only one had a fully completed succession plan.

Researchers found most baby boomer CEOs were postponing retirement because they didn’t have a qualified successor in their family, or wanted to maintain a high level control over their business, among other reasons.

"I think we often carry around this idea that there is a retirement age, and everybody is kind of fixed in on it," said Douglas Breunlin, a Northwestern University psychology professor who directed the study. Yet, labor statistics cited in the study showed the number of Americans working past the age of 66 is growing every year, he said.

"You've got sons now 55 years old who are ready to take the reigns and their 75 or 80-year-old fathers are still going like gangbusters," Breunlin said.