Casey Affleck, or How I'm Seeing Double

Casey 'Yes, my brother's name is Ben' Affleck had a great year in 2007. It has already been said that the double punch that was his lead in Gone, Baby Gone and his Academy-Award nominated turn in The Assasination of Jesse James by the Coward Robert Ford has now dispelled his 'younger Affleck' persona.
And yet, it seems Ed Harris and Brad Pitt are flummoxed by Casey's age:

Ed 'Love me some mousse-tache' Harris
How old are you kid?

Casey Affleck (circa Gone, Baby Gone)
31

Brad 'Jesse James' Pitt
How old did you say you were?

Casey Affleck (circa The Assas-longest title in the world-Ford)
20. Well I would be... but I guess that's not for another three months. So 19.

We agree Casey, you are looking good for your age. Keep up the good work!