I like those days, too! I think all the days are going to be lots of fun if we want to make them that way! And definitely some silly ones. :D
I think it's fine for anyone about 8 or 9 and up. It isn't written in such a way that it's incomprehensible if you're not bigger or older, but it isn't written like a small kids book. I mean, he's got children's stories, too, but I'm thinking of The Hobbit and so forth right now honestly. Mostly because that's what most people think of when they think of his works. It's written in a way that makes it accessible to most people so long as you like fantasy or don't mind that he gets super wordy sometimes. The cartoon for The Hobbit is rated 7+ and The Lord of the Rings cartoon is 9+. You could check those out, and, if you like them or want to see how the books differ, go from there? (Although 9 out of 10 times I'll recommend reading the source before seeing the adaptation.)