I think he has a great look for the role. He has a very theatrical child-man baby face. Perhaps by not physically fitting the part you mean he doesn't remind you of other actors who have played the role. So?
If the objection is that he isn't a typical leading man in looks, I find it an odd objection given that the role is at its core an Everyman (it certainly isn't archetypally a Prince in either the romantic or commercial traditions).
Beyond that, even assuming anyone would care, which they don't, no one knows what the actual Pepin of Italy aka Pippin aka Carloman looked like (and the images artists have provided over the centuries are quite dissimilar - as any google image search would reveal).
That he hasn't acted before doesn't mean that he can't act, particularly given that he's a performer.
Updated On: 9/19/14 at 11:00 AM