While Ted Kennedy and Michelle Obama were rocking the Democratic convention in Denver, John McCain made his 13th appearance with Jay Leno to joke about his age. McCain joked, "You forgot to mention that I warned the people about the British coming," and added, "my Social Security number is eight."

McCain has repeatedly tried to dismiss concerns about his age with late-night jokes. On Saturday Night Live, he quipped: "What should we be looking for in our next president? Certainly someone who is very, very, very old."

But McCain's age is no joke. He will turn 72 on Friday and would be halfway to 73 if elected and sworn in on January 20. That would make him the oldest first-term President ever, two years older than Ronald Reagan. He has survived four skin cancers (melanomas), including one in 2000 that was classified as Stage IIa.

McCain is two years older than his father was when he died suddenly of a heart attack at 70. He is 11 years older than his grandfather was when he died suddenly of a heart attack at age 61.

The United States cannot afford the risk that McCain would die suddenly in the middle of an international crisis.

Nor can we afford the risk of dementia. 22% of Americans over 70 are affected by mild cognitive impairment, while 13% of Americans over 65 have Alzheimer's. Ronald Reagan was diagnosed with Alzheimer's at age 83, but early signs were evident during his first term. Britain's "Iron Lady" Margaret Thatcher developed dementia at age 75.

Prescriptions can also adversely affect mental function. McCain takes Simvastatin, an arthritis drug that can cause memory loss. McCain also takes Ambien to sleep, which can cause amnesia and "fugue states" like the one that caused Rep. Patrick Kennedy's late-night car crash. If the phone rang at 3 a.m., would McCain even wake up?

McCain's medical records are not available to physicians. He did not "release" them for the campaign; he only allowed hand-picked reporters to examine them quickly without making copies. And there were no results of an Alzheimer's test, because McCain has never had one - even though he has 6 of the 10 warning signs, including his inability to remember facts like the number of homes he owns or the U.S. invasion of Iraq in 2003.

John McCain owes America a thorough test for Alzheimer's and cognitive impairment long before Election Day.