You don't want and you won't, even if you reach 100 years old.:-D
:-D I think this idiom means that if a person is six feet under is out of date.
He is six feet under= He kicked the bucket= He cashed in his chips= He died.
And another one: 'He's pushing up the daisies" (Pushing up the daisies - Idiom Definition - UsingEnglish.com ) Same idea.
But why 6 feet? I've heard it said that a scavenging animal could smell a rotting corpse in a shallower grave, but I'm not sure about that.
Because it is the traditional depth of a human grave in the culture(s) of origin and usage of the idiom.
I found this at The Straight Dope - Fighting Ignorance Since 1973 under the title, "Why is 'six feet under' the standard depth for burial?
That settled, where did the famed figure come from? Historians believe it dates to London's Great Plague of 1665. In Daniel Defoe's fictionalized account A Journal of the Plague Year, the diarist-narrator reports on an edict issued by the city's lord mayor in June 1665 requiring that all graves be made at least six feet deep to limit the spread of the outbreak. Even if Defoe's research wasn't perfect (his firsthand knowledge may have been less than reliable, as he was only five at the time of the epidemic), other sources largely back up his version of events; in any case, his book likely popularized the notion that proper burial entailed putting the body six feet under.
As a reward to myself for having resisted making lots more burial-related puns, I'll just mention that lawyers are buried 24 feet underground rather than 6. Why? Because deep down, they're real nice people.
Colman, Penny, Corpses, Coffins, and Crypts: A History of Burial (1994)
Iserson, Kenneth, Death to Dust: What Happens to Dead Bodies? (2001)
Jackson, Percival, The Law of Cadavers and of Burial and Burial Places (1936)
True? Not? Who knows?
I learned this idiom from one song.
We have the same in Pakistan. Though we usually use ''... the earth''.
''chhay fut zameen talay'' -- six feet under the earth.
The other idioms that relate to being dead that I know of are ''kick the bucket. give up the ghost, join the great majority, snuff it, meet one's maker, to be in the other world/gone/no more/over and done with/kicking the daisies''. And ''his/her days are numbered, got one's feet in grave'' for being near dying.
they are dead.