A floating timeline (also known as a sliding timescale) is a device used in fiction, particularly in comics and animation, to explain why characters age little or not at all over a period of time - despite real-world markers like notable events, people and technology appearing in the works and correlating with the real world. A floating timeline is a subtle form of retroactive continuity. This is seen most clearly in the case of comic book characters who debuted as teens in the 1940s or the 1960s but who are still relatively young in current comics. Events from the characters' pasts are alluded to, but they are changed from having taken place years ago to having taken place more recently.
Any dates given within the comic are not relative to the publishing date of the comic (i.e. "10 years ago" means "10 years before you read this"). This device enables publishing companies to continue to use their characters for as long as they wish without changing them significantly. A floating timeline is usually abstracted from that of actual historical events, but may contain subtle references to the real world timelines.
For example, mystery writer Rex Stout created a floating timeline for master detective Nero Wolfe and other principal characters in the corpus, while the stories take place contemporaneously with their writing and depict a changing landscape and society. Nero Wolfe's age is 56. "Those stories have ignored time for thirty-nine years," Stout told his authorized biographer John McAleer. "Any reader who can't or won't do the same should skip them. I didn't age the characters because I didn't want to. That would have made it cumbersome and would seem to have centered attention on the characters rather than the stories."  In the early novels, Wolfe dated himself somewhat by discussing his life before World War I and his combat service in that war, but in later stories he was less explicit about his past.
- McAleer, John, Rex Stout: A Biography (1977, Little, Brown and Company; ISBN 0-316-55340-9), p. 383; and McAleer, John, Royal Decree (1983, Pontes Press, Ashton, MD), p. 49