The traditional retirement age for CEOs at IBM has been 60, or close to it.
Palmisano isn't stepping down because of apparent displeasure by the board, of which he is chairman. He is leaving after having set a strategic direction for the company through 2015.
But there is a logic to a relatively early retirement by a CEO, and not just at IBM .
The average age of a departing CEO is 61, according to The Conference Board, in a report this year on CEO succession. It calculated this figure after studying CEO turnover among companies listed on the Standard & Poor's 500 ranking of the largest public corporations.
That average age represents both retirements and those CEOs who, for one reason or another, were forced out of their jobs, likely in their 50s, according to Jason Schloetzer, an assistant professor of accounting at the McDonough School of Business at Georgetown University and an author on the study.
Most companies adopt mandatory retirement ages for a CEO between 62 and 65, Schloetzer said.
An early CEO retirement can be beneficial to a company by making it "clear to the people reporting to the CEO that if they work hard, the promotion potential is there," Schloetzer said.
If a mandatory retirement age is, for instance, 75, it becomes unclear when a person may depart as CEO. That may prompt some top managers to seek advancement at another company, or they might lose the incentive to work hard to distinguish themselves as someone who could succeed at the next level, Schloetzer said.
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