Logan's run
A future world ruled by youth, where life ends at 21. If you try to escape this fate and run, you are pursued by Sandmen, the hired guns who enforce the "death at 21" rule. Our hero, Logan, is a Sandman. And he decides to run.
Fiction, Logan (Fictitious character), science fiction, dystopian, Sandman
William F. Nolan, George Clayton Johnson
About the Author
William F. Nolan is best known as the creator and coauthor of Logan's Run, a bestselling science fiction classic that was made into a hit film, a television series, and a sequence of comic books. He is the author of 13 novels and scores of short stories, and is the editor of more than two dozen books in the fields of science fiction, horror, western, and suspense. He is a two-time winner of the Edgar Allan Poe Special Award from the Mystery Writers of America and was voted the Living Legend for 2002 by the International Horror Guild. He lives in West Hills, California.

Info added Nov2012, from amazon & wiki: 
* http://www.amazon.com/Wild-Galaxy-Selected-Science-Fiction/dp/1930846312/
* http://en.wikipedia.org/wiki/William_F._Nolan