Yes, Theon is around that age. Collin is older, but there are not to many fitting actors in the age of 19...well, probably there is, but anyway I do not know their names.
I would also like to see more brittish actors...I always imagin westerosi speaking brittish dialect (The wildling speak scottish dialect in my mind), any suggestion of fitting brittish actors? I would want Antony Head for exampel, but I don't know in what role...
What's wrong with Dakota Fanning? I think that she is a great actress, and there are'nt really alot of those in the age of ten. And I really want a talented actress to play the role of Arya... And I do think that Buscemi would make a great Rattleshirt.
The problem with unknowns is that it's quite hard to make a list of those, because they are...well, unknown.
If there would be a movie (I doubt it), I too would like many of the characters to be played by rather unknown actors, otherwise it would get *real* expensive. But this is just fantasy, the budget of our mind is endless.