My older three all love books, and I think Thomas is catching on too!
He can pretty much always be found pulling the books off of the book shelf, and I don't usually stop him (unless he's ripping them or something, of course!). I want him to always feel drawn to the books. I guess it's kind of like my mom says with her piano - as long as the kids aren't being rough with it, they are welcome to play it. I don't want to kill his curiosity by telling him "no" to touching the books. I want him to always be drawn to them. Besides, that's why we have a kid book shelf anyway!
(As I post this he's behind me emptying the bookshelf!)