THE SEPTUAGENARIAN ISSUE…. It’s hard to say how seriously voters consider the issue of John McCain’s age and health, but this poll will probably raise some eyebrows among McCain’s aides.

It’s one of the largest age gaps between presidential candidates in American history.

Republican Sen. John McCain is 72, a skin cancer survivor, and would be the oldest man sworn in for a first term as president. His opponent, Democratic Sen. Barack Obama, is 47 and the fourth-youngest major party nominee.

A new CNN/Opinion Research Corp. Poll finds that may be a political liability for McCain. Nearly half of the Americans surveyed, 47 percent, are concerned that McCain would not finish a four-year term as president in good health.

In a competitive race, when nearly half the electorate is worried about a candidate’s ability to serve a full four-year term, that’s an issue that might matter. Indeed, the CNN poll showed that more than a fourth of voters (29%) said they are “very concerned” about McCain’s ability to complete a first term.

What’s more, one-in-five respondents to the poll said McCain’s age would be a factor when they voted. (One assumes, under the circumstances, that for most of these people, won’t be more inclined to support McCain given his septuagenarian status.)

I could be wrong, but I don’t recall this question being polled in any of the recent presidential campaigns. (Was anyone worried that Bush and/or Kerry might not be able to finish a four-year term in good health?) Then again, McCain would be the oldest president ever elected, and he does have the most ridiculous running mate in modern political times, so I suppose the question is hard to avoid.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.