The issue of the 72-year-old U.S. senator from Arizona's age has been raised by critics who say Alaska Gov. Sarah Palin, his 44-year-old vice presidential running mate, is unqualified for the job.

Insurance industry actuaries say men who are 72 have a 33 percent chance of not surviving to reach 80, which would be McCain's age at the end of possible second term, the Washington Web site Politico reported Wednesday.

"Actuarial models are good for estimating the average future lifetime of, say, 100,000 50-year-olds, or how many out of 100,000 50-year-olds will survive to 60, but are lousy at estimating about one particular 50-year-old," Jim Daniel, a professor of actuarial studies at the University of Texas, told Politico.

Other experts said McCain's history of skin cancer might affect his survival odds.

"It's not just a matter of McCain being age 72," Lois Horwitz of Boston University told Politico. "It has to do with, of course, the underwriting characteristics of their lives."