The best books aren't static stories, but living entities with meanings that change and grow along with you. That's why we strongly recommend rereading the classics that were assigned to you in high school; you may find that they're nothing like they were before.
Still, some books are best experienced at a certain age, like, say, "Catcher in the Rye." If you pick it up for the first time when you're far beyond puberty, you'll likely wonder what all the hype is about. Likewise, there are certain books you should read in your 20s, due to the age of the characters or the intended audience -- books like Donna Tartt's "The Secret History" or Christopher Hitchens' "Letters to a Young Contrarian."
Check out the 30 books we think you should read before you're 30: