On approaching his 60th birthday this year, long-serving Tullow Oil boss Aidan Heavey told staff he felt “like two 30 year-olds.”

A handful of recent shock departures by 50-something chief executives at European blue chip companies—none of them under any obvious pressure to quit—suggest some of his peers either lack that vigor, or want to channel it elsewhere.

Peter Voser is giving up one of the world’s most challenging CEO roles at Royal Dutch/Shell next year, before his 55th birthday, in pursuit of a “lifestyle change.”

Swiss engineering group ABB’s 55-year old boss Joe Hogan is also going, for “private reasons.” Pierre-Olivier Beckers, 53, is walking out on Belgian retailer Delhaize, and Paul Walsh, 57, is waving goodbye to drinks multinational Diageo.

All four are about-average European CEO age.

Luxury goods group Richemont’s chairman and founder Johann Rupert, older than the rest of the May retirees, at 62, gave up the CEO post in April and on Thursday announced he would take a year off from the chairmanship, too, to catch up on some reading—and perhaps a trip to the Antarctic.

While the rising financial rewards of running a modern multinational have been well publicized, executive recruiters say the pressures of the job have also been ratcheted up in recent years, and not just because of the tough economic times.

“The reality is it’s grueling. It’s really tough, and there comes a point where you don’t want to do it anymore,” said Ian Butcher, who headhunts board-level and senior executives for MWM Consulting.

“The quarterly reporting, the governance, the regulatory aspects, it just becomes very wearing—the level of scrutiny, the pace at which things are moving, the short-term nature of how people look at any given situation. Even over the past five years these things have made CEO a tougher position to hold, and the travel that people have to undertake in these jobs—it’s just something they run out of steam on.”

“I just want to be master of my time for some time,” said Richemont’s Rupert.

Some recent early retirees, while still well short of traditional retirement age, got to the top spot early.

“They’re still in their early 50s, with energy and a desire to do something, but they want to do something different, something quite significantly different sometimes,” says Butcher.

Voser might not be donning snow shoes for an Antarctic venture, but he has no plans to collect well-paid chairmanships and non-executive directorships, as many ex-CEOs have done in the past. Former Tesco chief Terry Leahy has also resisted that gravy train since he left two years ago.

As for the early starters, executive search industry professionals point at people like Andrew Witty, the CEO of GlaxoSmithKline, who took on the job aged 44 in 2008 and would have to stay in harness for another decade to reach 60 in the role.

Blue-chip bosses as young as Witty are still rare, but over a quarter of Europe’s current crop have less than two years in the job, and more than half have less than four, according to data from executive search specialists BoardEx.

Median CEO Age Is 55 Years

The BoardEx data, collected for Reuters from 238 companies in the main stock indexes of Germany, Britain, France, Spain, Italy, Belgium, the Netherlands and Denmark, puts the median CEO age at 55, and the median tenure at four years. Only 16 percent of the group have held on for 10 years and more.

The longest serving of them is Martin Gilbert of the British fund Aberdeen Asset Management. Although younger, at 57, Gilbert tops the 28.3-year tenure of Tullow’s double thirty year-old Heavey, with 29.8 years at the helm.

There are 17 top European CEOs who have been in the job for less than six months, and the youngest of the 225 in the group for whom ages were available is Vitaly Nesis, 37, who runs Polymetal International, the London-listed Russian precious metals miner.

While the recent spate of quitters are looking for something else to do, there are still some who appear to want nothing but.

In the BoardEx group there are four over 70, and the oldest by eight years is Albert Frere, CEO of Group Bruxelles Lambert.

Perhaps some linger on for fear that the pension pot is still a little light. Frere will have put such qualms behind him long ago. At 87, he is Belgium’s richest man.