OK he might have looked 13
Oh James MacAvoy is rather lovely and nearly thirty now so he wouldn't be that much too young given that slower hobbit aging.
I always thought Michael C.Hall would have been a good Bilbo - his portrayal of David Fisher in Six Feet Under had that hard combination of prissiness, courage and compassion... but I suppose his more recent role as Dexter the serial killer would make that an eccentric choice..... I still think he looks a bit hobbitty and at 37 he is just about the right age.