Living on borrowed time
Living after the time you would have expected to have died.
In 17th century England it was usual to describe the first eleven days of May as borrowed days, because in the Old Style calendar they belonged to April. Sir Thomas Browne referred to this in Pseudodoxia epidemica, 1646:
"So it is usual among us... to ascribe unto March certain borrowed days from April."
Borrowed time isn't from that source though - this is time 'borrowed' from Death, that is, after when one might have expected to have died. The term was known in the USA by the 1880s; for example, this piece from The Indiana Progress, September 1886:
"We may be care-worn and aged, forsaken of the world, living on borrowed time, useless so far as any activity is concerned, dependent on children, or friends; yet Jesus has loving acquaintance with us."
In 1898, The English Dialect Dictionary defined the phrase:
"A man who lives on borrowed time lives on trespass-ground."