This video shows the funny - and expletive-filled - reaction of a 98-year-old man as his son gently reminds him how old he is.

The son, YouTube user Pinball Wiz, starts by asking his father "How old do you think you are?" His dad replies that he is just 79.

When prompted to try again, the father guesses at 89, then continues year by year until he gets to the right age.

He reacts with horror and shock. "Your ass, I am not 98 years old. Holy f**k. That is old. How did I get so old so fast?"

His son replies with the age old cliche: "Time flies when you're having fun."

"Next year I'll be 100! Holy f**k. Jesus, I'm going to be an old f**king man!" he replies dad.

The video has been viewed on YouTube more than 660,000 times in two days and has received hundreds of comments.

One Reddit user wrote: "Yes you're gonna be an old f**kin man at 99 years old. But not yet lol. It truly is that you're as old as you feel."

Another user posted: "'How did I get so old so fast?' That statement right there is a terrifying revelation at how fast life can pass you by."

A third said: "This is very endearing, thank you for posting this. As a 30 year old already terrified of aging, this is comforting and both scary at the same time. Your father is lucky to have you, I'm sure he was a good dad, too."

The old man was praised for having such high spirits at his age and was called a "legend" and a "beauty" in YouTube comments.