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The most powerful man in the world turns 60 on Thursday and he just can't seem to stop talking about it. Barely a week has gone by this year that President Bush has not brought up his advancing age at least once.

"How you doing, sir?" a reporter asked Bush at a news conference a few hours after a middle-of-the-night return from a grueling sprint to Baghdad. "I'm doing all right, thank you," the president replied. "A little jet lagged, as I'm sure you can imagine. Nearly 60."

In his State of the Union address, the president referred to his upcoming birthday as "a personal crisis." It was a laugh line — used to segue to a call for overhauling programs, such as Social Security and Medicare, soon strained by Bush's baby boomer generation.

In fact, Bush is nearly always cracking wise when the topic of his age comes up. The humor, however, contains unmistakably wistful notes, revealing a president who is least somewhat pensive both about aging and his relevance after he leaves the White House in 31 months.

Bush's "I'm getting old" preoccupation puts him in good company.

Cher, Bill Clinton, Dolly Parton, Donald Trump, Sylvester Stallone, Diane Keaton, Suzanne Somers, Reggie Jackson and Jimmy Buffet also are turning 60 in 2006. They are part of the first wave of the 78-million strong baby boomers to enter their senior years.

Karl Pillemer, a professor of human development at Cornell University, said the president's musings are reflective of the group.

Boomers brought advances in the civil rights and women's rights movements. But the generation also introduced America to what Pillemer called "the new narcissism." And now, members of this group are presented with a slew of sometimes bewildering roles: seeing their children enter adulthood; contemplating grandparenthood; watching their parents age and die; retiring from work; and dealing with physical and intellectual limitations.

"For many boomers, turning 60 is a fairly significant shock," Pillemer said. "The generation that believed it would be young forever, clearly will not. ... The boomers are having a hard time with the existential reality of life not being one open-ended opportunity after another."

Dr. J. Edward Hill, the immediate past president of the American Medical Association and a family physician from Tupelo, Miss., has seen many patients display Bush's chatty angst. But he said the president's joshing around is one of the healthiest approaches.

"When you worry about something, you talk about it," he said. "The stints of humor are critically important."

In speech after speech, Bush has referred to himself as the "old president — getting older by the minute, by the way"; as one of "the gray-haired folks"; as "getting older"; and as just flat-out "old."

He often reflects on how he considered 60 practically ancient as a younger man, but has been inspired by changing circumstances to adjust his perspective. "It's all in your mind," he said recently in Omaha, Neb. "It's not that old, it really isn't."

"When are you turning 60?" he quizzed Pete Navarro, a somewhat wrinkled Florida man participating with the president on a panel in May on Medicare's new prescription drug benefit. Bush deflated a bit when Navarro reported that his 60th birthday was not until next January. "Oh, January. You're a lot younger than I am," the president said.

Most often, the famously competitive and fitness-crazed president brings up the physical ravages of time. He jokes about losing his hearing (a frequent source of ribbing by his staff as well), about how knee problems turned him to riding his bike after years of jogging, or about how he is too old for the basketball court.

Bush even broods aloud about his life expectancy, estimated to be an additional 19 years for the average American male his age. "I don't know about you all, I plan on just kind of stretching it out a little bit," he told GOP donors in Indiana in March.

Like most presidents, Bush has grayer hair, more lines and a few extra pounds than when he took office. Yet he still has the health statistics and energy of a much younger man.

Those close to him say Bush is entirely comfortable with the milestone, in part because of the discipline that allowed him to turn 20 years ago from a life of excessive partying and career meandering and never look back.

He also revels in remaining in shape, even markedly improving his fitness, thanks to intense, six-days-a week workouts. The president may have traded running shoes for a mountain bike, but he pushes himself hard, so much so that he has made news several times when hairpin rides sent him tumbling to the ground.

"I'm sure it makes it easier, especially when you're whipping people half your age — some of them trained to kill people, like Secret Service agents," White House counselor Dan Bartlett said.

The president's most recent physical, conducted last July, found he had a resting heart rate in the range of a well-trained athlete and nothing worse than mild hearing loss, skin lesions from sun damage, occasional acid reflux and joint stiffness. His physicians placed him in a "superior" fitness category for men his age.

Age milestones are common for commanders in chief.

Ten other presidents have turned 60 in office. Dwight Eisenhower had his 70th birthday in the White House, as did Ronald Reagan. Seven others turned 50, including Clinton.

The president's 60th celebration looks barely different from other recent birthdays, just a bit bigger.

About 150 close friends and family are dining with Bush and his wife, Laura, who turns 60 herself in November, on July 4 in the White House residential quarters. Afterward, they will gather on the Truman Balcony for Washington's dramatic fireworks show — and no doubt keep Bush from his usual 9 p.m. bedtime in the process.