WASHINGTON (AP) — So how old is John McCain? Six-packs, automatic transmissions and the American Express card were all introduced after he was born — not to mention computers, which McCain admits he doesn’t use.

McCain, himself, jokes that he’s older than dirt. And while his age is being raised as a campaign issue, medical experts say voters shouldn’t be concerned that, if elected, McCain would be the oldest man to assume the presidency, at 72.

In politics and other fields, they explain, it’s not unusual for talented people to do signature work late in life, when they can apply the cumulative wisdom of experience, and leverage personal connections cultivated over time.

Nonetheless, a significant slice of the electorate has qualms about McCain’s age. The presumed Republican nominee will celebrate his 72nd birthday shortly before his party’s convention. Polls show the age question isn’t going away, despite the Arizona senator’s efforts to deflect it with self-deprecating humor, or disprove it by keeping a grueling schedule.

“Sure, people live to be 90, but you are not as sharp,” said Virginia Bailey, 73, a retired administrative assistant who lives near Schenectady, N.Y., and is a Republican. “I’m not as sharp as I was ten years ago, and I’m sure (McCain) isn’t either — even though he wouldn’t admit it.”

McCain’s senior-citizen status raises more concerns among voters than Sen. Barack Obama’s relative youthfulness, a new AP-Yahoo News poll indicates. Twenty percent said “too old” describes McCain “very well,” compared with 14 percent who felt strongly that Obama is “too young.” Overall, 38 percent said “too old” describes McCain somewhat or very well, compared with 30 percent who worried that the Illinois Democrat, who turns 47 this summer, is too young.

An expert on the presidency and professor of communications, Leonard Steinhorn, of American University in Washington, said McCain is “getting on the upper end of the comfort zone for Americans, who wonder whether he’s going to have the vigor and the health as president. “

Capitalizing on such concerns, New York City graphics designer Joe Quint has launched an Internet site called thingsyoungerthanmccain.com. Quint, a Democrat, said he doesn’t believe septuagenarians should be disqualified from the presidency, but age should be part of the discussion. He’s planning a book of his Web site items before the election.

Medical science, however, suggests that concerns about McCain’s age are exaggerated.

“The presidential campaign is full of chatter — much of it quite misinformed — about the role of age,” said Dr. William Thomas, a geriatrician and professor at the Erickson School of Aging Studies at the University of Maryland, Baltimore Campus. Geriatrics is a medical specialty that focuses on the elderly.

“People in old age are fully capable of imaginative and skillful work,” Thomas added. “A person’s age is not a block to doing fantastic work.”

Although U.S. life expectancy at birth is about 78 years, a person who reaches 70 can expect to live another 15 years. For a seventy-something president, that could work out to two terms in office, plus time for writing memoirs—and cashing in on book sales.

But differences among people in their seventies can be stark, because some have already started into a steep decline.

Dr. David Reuben, chief of geriatrics at UCLA’s David Geffen School of Medicine, said he sees no outward evidence of such a problem with McCain, despite the occasional gaffe.

“As a clinician, I look at whether they appear to be robust, whether their sentences flow, whether their thoughts connect, whether they are easily distractible,” said Reuben. “McCain appears to be quite robust.”