In her new memoir A Swim-On Part In The Goldfish Bowl: A Memoir, Carol Thatcher revealed her mother Margaret Thatcher started showing signs of dementia in 2000, at the age of 75.

"I almost fell off my chair," wrote Thatcher, a journalist and television personality. "Watching her struggle with her words and her memory, I couldn't believe it. She was in her 75th year but I had always thought of her as ageless, timeless and 100 per cent cast-iron damage-proof. From the fateful day of our lunch, tell-tale signs that something wasn't quite right began to emerge."

John McCain turns 72 on Friday. Like Thatcher, he wants us to think of him as "ageless, timeless and 100 per cent cast-iron damage-proof." Sadly, no one is - not Thatcher, not Reagan, and not John McCain.

McCain's age is already an issue in the campaign due to McCain's repeated "senior moments," most recently not knowing how many homes he has. At age 72, McCain would be the oldest President ever sworn in. A new Washington Post poll shows 44% of voters are concerned about McCain's age, and they are right to be concerned: 13% of Americans over 65 have Alzheimers, while 22% of Americans over 70 have a cognitive impairment.

Obviously McCain's age is a huge risk for the country. Shockingly, McCain had no mental evaluations in the past eight years. McCain owes it to the country to take an Alzheimer's test and share the results with the American people before we cast our votes.