The theme will be an understated one, with more of a vintage-y feel... coming more from little objects in the room than any blaring bedding or wall decor...
Owls.
They are my favorite animal and I am just getting this "feeling" that it will suit this little mister well. Here are some things that I already have around the house that will make great additions:

Beyond this, maybe a couple more vintage owl prints for the walls and an amazing stuffed owl or two along the lines of these:

Found here.For the bedding, I'm thinking solid cream or white with a vintage quilt to top it all off.
Simple. Clean.
You know... totally hoot-tastic.