Looper (the upcoming movie)

Does any one else think that it's a little hard to believe that Lil' Joesph Gordon-Levit could possiably play a younger version of Bruce Willis? I've seen the trailers, the movie looks pretty cool to be honest, but it's still hard for me to wrap my mind around it. It's just that Joe is so small and Bruce is a pretty good sized guy? What do you guys think?