Washington ? John McCain, 70 and scarred, cannot deny his age. So he jokes about it.

“I’m older than dirt, more scars than Frankenstein, but I learned a few things along the way,” quips the Republican presidential candidate, who tries to play down the ravages of time for the wisdom acquired over his seven decades.

His body is battered from torture in Vietnam. The scar along his left cheek is a reminder of a different battle, with skin cancer. Yet, McCain packs his work days so tight that aides grouse. And the man who could be the oldest first-term president hiked the Grand Canyon from “rim to rim” last summer.

Despite McCain’s high-energy lifestyle, getting older begets questions about health. The four-term Arizona senator no doubt will have to prove to voters that he is physically and mentally up to the demanding job of president.

Republican presidential hopeful Sen. John McCain of Arizona shakes hands with Safety Commissioner Richard Flynn during a campaign stop Sunday in Dover, N.H. McCain, 70, has been facing questions about his age.

For now, the issues are only background murmurs in the 2008 race for the GOP nomination.

Neither Rudy Giuliani, the 62-year-old former New York City mayor who also is a cancer survivor, nor former Massachusetts Gov. Mitt Romney, a diet-and-exercise fanatic who just turned 60, has mentioned them publicly.

Still, an aging candidate troubles some voters.

Two recent surveys found that people are less likely to vote for a presidential candidate who is older than 72 than they would a candidate who has been divorced twice and a candidate who is Mormon.

Giuliani is on his third marriage; Romney is a member of the Church of Jesus Christ of Latter-day Saints.

In Michigan, Jerry Roe, a Republican who is a former state GOP executive director, backed McCain in 2000 but supports Romney this time. “McCain’s too old,” said Roe, whose son is a deputy campaign manager for Romney.

“He looks tired. He looks like he’s dragging,” added Chip Felkel, a GOP strategist in South Carolina who says he is not aligned with a candidate.

McCain is determined to counter the notion that his age and health are hurdles for his campaign, and he does not hide his distaste for the topic when questioned.

“I work seven days a week, 16-plus hours a day. I’m fine. I’m in great health,” McCain tells anyone who asks.

Now 83, Bob Dole recently said McCain will face “constant questions about his fitness and ability to serve.”