I had to pick up the Cinefex that just came out because the effects were so fascinating to me. And it turns out there's a reason that some of us didn't connect with Pitt's performance - it wasn't all him. They did the early Benjamin with other actors as the body and they did performance capture on Pitt for the acting. So really the Benjamin from birth to appearing age 69 were all different actors and the face was done like Gollum or Yoda.
One of my main problems was with the body movement - so I can't blame Pitt for that. But I wouldn't have thought those weren't Pitt in makeup - so there was truly some groundbreaking CGI going on.
It looked CGI to me, but it was indeed good. In the closing credits it listed who played Benjamin from when to when and there were two, I think, that played him when his was younger (old man).