The hero of Doorways In The Sand has managed to stay in college for something like 14 years without graduating. He gets close at times, but always changes majors or otherwise manages to escape. The reason is that his uncle's estate pays for his college education until he graduates, but doesn't contain a time limit.
As books by Zelazy go, Doorways In The Sand is good, but not one of the greats. It's fluffier than something like Lord of Light, and lacks the grand sweep of the Amber Chronicles. Still, it's fun and well written. Definitely worth your time if you're into lighter SF.