Washington ? Sen. John McCain, of Arizona, will do something next week that’ll set him apart from everyone else who’s weighing a run for president in 2008.

He’ll celebrate his 70th birthday Tuesday.

That would put him in uncharted political territory should he win the presidency: No one older than 70 has ever moved into the White House.

Not only will the Republican senator be the oldest of the large field of possible candidates in both major parties, he’ll be three years older on Election Day 2008 than Ronald Reagan was when he won his first term in 1980. At 69, Reagan was the oldest man ever to enter the White House. He was 73 when he won his second term.

Whether this changes the presidential campaign probably will depend on whether McCain appears healthy and vigorous – and thus up to the unique demands of the job.

McCain aides said the senator was cancer-free six years after surgeons removed thin tumors from his temple and arm. Both were diagnosed as malignant melanoma, a potentially deadly form of skin cancer if left untreated. He also had a bout with skin cancer in 1993.

And they say he’s more energetic than many much younger men.

“His health is fine,” said John Weaver, his chief political strategist.

“Just this month, he backpacked the Grand Canyon from rim to rim with his son, he went on a weeklong tour campaigning for people and he’s about to lead a delegation on a multination tour of Eastern Europe.”

Veteran Richard Danielson, right, talks with Sen. John McCain, R-Ariz., on Monday after an appearance at Cuyahoga Community College in Parma, Ohio. McCain is traveling the state with Sen. Mike DeWine's re-election campaign.

Weaver noted that McCain still would be younger than Reagan was when Reagan sought and won his second term. He also stressed that McCain is a key player in the Senate, where he’s involved in numerous issues and negotiations.

In time, he suggested, voters will see for themselves.

“They’ll see that if he chooses to run. They’ll see how vibrant he is.”

If that’s not enough, Weaver also suggested considering McCain’s genes.

“His mother, at 95, just returned from Europe, where she keeps a car and drove herself across the continent,” he said. “He comes from good stock.”

Yet it’s not just the state of a candidate’s health on Election Day that matters. The elderly face a greater risk of developing problems in the years ahead, including heart disease, stroke, cancer, infection, Alzheimer’s or even death.

“No matter how healthy the elderly candidate for the presidency appears to be, there is a significant likelihood that he will not survive or that his intellectual powers and leadership ability may be compromised, far more so than among those in their 50s,” two Stanford University scholars wrote in a study after Bob Dole’s 1996 presidential campaign, when Dole was 73.