But the tenures are much the same. The average CEO of a large company lasts six years, Gaines-Ross says, and 27% of CEOs are gone within three years, according to a study out in June at Rice University.
However, companies like to gamble on the 1-in-20 chance of a 20-year success story, and that won't happen if they bring aboard a septuagenarian.
Young CEOs sometimes acquire a lifetime of experience early in their careers. Pulte CEO Dugas started running the home builder before the ongoing 30-month housing depression began. The company's stock bottomed out at $8.20, down from $46.74 in July 2005. It closed Tuesday at $12.47. Dugas finds himself leading through a business crisis worse than most CEOs see in a career.
Such downturns can make leaders prematurely gray. But gray hair has its advantages, Miller says.
"I don't think you get smarter, but you get wisdom. Everything is not an existential crisis. When you get older, you separate out what is really a crisis from an average problem," Miller says.
The stock price of Universal Health Services hit an all-time high this year, and Miller, 70 and CEO for 30 years, signed a five-year extension on his contract in December.
Character and courage are more important than age, Miller says. "If you're a young weasel, you'll be an old weasel."
Contributing: Matt Krantz