[Charles Henrickson]

other characters have yet to be decided.

I suppose you folks in the Hobbit Hole have discussed casting already, but the guy I would like to see cast as Bilbo is James McAvoy. I think he'd be perfect. But he may not want to do it after playing Mr. Tumnus in Narnia and being a hot property after Atonement.

[HairOfTheDog]

I’ve seen him mentioned for Bilbo. He is very hobbity.

We haven’t discussed a LOT of casting issues... mostly just figuring out which actors might return. Aragorn, even for some bit parts... Legolas too I hope could come back, just to give the continuity to the whole series.

[SuziQ]

I really don't see why Ian Holm couldn't come back as Bilbo, if he wanted to do it. In the flashbacks in the Trilogy, Ian Holm is wearing a wig that's slightly darker, but, at the beginning of the Fellowship of the Ring, when Bilbo opens the door, Gandalf hugs him, then says, with a curious tone, "You haven't aged a day!"

So, if at the beginning of the trilogy, Bilbo looks the same age as at the end of the Hobbit, because of the effect of the One Ring, I don't see why Ian Holm couldn't play him. The filmakers could 'age' him slowly through the Hobbit, to match with the younger, then older Bilbo in the Trilogy.