Elvis Presley would have been 75 today -- had he not died of drug-induced heart failure at the age of 42.

My reaction -- and the reaction of other people I talked to -- was "Really? He would only be 75?"

That makes him 21 years younger than fitness guru Jack LaLanne, two years younger than Elizabeth Taylor, and only eight years older than Paul McCartney.

So why does Elvis seem like he should be so much older than he is? I would bet that it's because he spent his later years as a washed-up caricature of his former vitality. Elvis famed '68 Comeback Special aired when he was just 33.

By comparison, John F. Kennedy was assassinated in the prime of his career, when he was still a symbol of youthful vigor and virility.

As a quick experiment, I asked a few baby boomer friends how old they though John F. Kennedy would be if he were alive today? Everyone guessed that he would be in his late 70s or early 80s. The reality? John F. Kennedy would be 93. But the image of him as a young man is what sticks in people's minds and, consequently he seems younger than he is.

Moral of the story? If you want people to constantly think you're younger than you are after you die, stay away from drugs and alcohol, and be a symbol of youth during your life.