Well I don't know a bunch about 21 year-olds. But i read this great series by Andrew Klavan called The Last Thing I remember. It's a book about a fugitive and terrorists. The main character's got a little humor i guess. It's worth a shot anyway.
You can read any book by Sidney Sheldon. Some of them include: The naked face, A stranger in the mirror as well as Bloodline. Her books are full of love and betrayal, vengeance and redemption and they are fun and interesting to read.