> how old

It formed an essential ingredient of Ian La Fresnais & Dick Clements' script for Porridge which starred Ronnie Barker as a convict - it allowed a swear-word euphemism on prime-time (Sunday evening?) family TV. I seem to remember it gained even further prominence when it was adopted by Princess Anne on one notable occasion when talking to a journalist.

Ronnie Barker always claimed to have coined the word, but I believe it actually comes from Polari, the gay and actors' coded language. Although probably backronymic, some commentators have claimed it was code for "not available for fucking"; whether true or not, it certainly was used to describe straights in Polari.