Murtha is 75, four years older than McCain. He says they are nearly the same age, and the rigors and stress of running the country is too much for guys their age.
"I've served with seven presidents," Murtha told a union audience. "When they come in, they all make mistakes. They all get older."
"This one guy running is about as old as me," he said, drawing laughter and applause. "Let me tell you something, it's no old man's job."
If elected, McCain would be the oldest man to become president at age 72. Ronald Reagan became president at age 69, but he served as president for eight years and was just a few weeks shy of his 78th birthday when he left office.
Murtha, a Democrat from Pennsylvania, made the comments while introducing the candidate he has endorsed, New York Sen. Hillary Rodham Clinton, to the AFL-CIO's Building Trades National Legislative Conference.
Clinton referred to Murtha's introduction when she took the stage, saying she was grateful to have his endorsement and agreed with his sentiment that it will be difficult to turn around all the damage of the Bush administration. She didn't mention his comments on McCain's age, and the campaign sought to distance itself from the comments.
Clinton spokesman Mo Elleithee said Clinton "considers Senator McCain a friend, and she respects him. But it's not his age she has a problem with, its his ideas for the future."
Earlier this week, McCain was asked about his age and he joked about it, at first feigning sleep.
"Watch me campaign. We keep a heavier schedule. We campaign harder," he said Monday during The Associated Press annual meeting. "People will judge me by my performance. I am confident that my energy, my intellect, my experience, and my judgment is what American people will — hopefully that they will view me as qualified to be president of the United States."
His campaign said Wednesday Murtha's comments were "nonsense attacks."
Of the Democratic candidates, Clinton is 60 and Sen. Barack Obama is 46.
McCain and Murtha are both Vietnam veterans who have worked closely on national security issues. Age hasn't slowed Murtha down. After Democrats took control of the House in the 2006 election, Murtha sought the House majority leader position but was defeated.
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