The story
The phrase (not the acronym) "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 of the acronym from 1993, in a trademark filed for YOLO gear with "you only live once" in small lettering. The acronym was popularized around 2011 by Canadian rapper Drake. YOLO was entered into the Oxford English Dictionary as a word on September 12, 2016.
Etymology from Wiktionary, CC BY-SA 4.0.