The phrase "you only live once" dates to the 19th century according to research by Katherine Martin, head of U.S. Dictionaries at Oxford University Press. It saw a steady increase of usage from 1940 to 2000. Ben Zimmer, lexicographer, found the earliest usage from 1993 in a trademark filed for YOLO gear with "you only live once" in small lettering. 
YOLO was entered into the Oxford English Dictionary as a word in 2016. 
- (slang) you only live once, i.e. expressing the view that one should make the most of the present moment.
- Making this cake mix eleven years past the expiration date, because YOLO!
- Alyssa Bereznak, "An Oral History of YOLO, the Word That Lived Too Long", Vanity Fair, February 5, 2013
- ^ "Moobs and YOLO among new words in Oxford English Dictionary", BBC News, September 12, 2016