From Producer Gaston Pavlovich:
You don’t use prosthetics, make-up; they have acting and the technology is able to have them go through different time ages without the prosthetics. So we’ve seen some tests and it looks extraordinary. We were able to film Bob and just do a scene. We saw it come down to when he was like 20, 40, 60, so we’re looking forward to that, from that point of view, for The Irishman … Imagine seeing what De Niro looked like in The Godfather: Part II days, that’s pretty much how you’re going to see him again.
I think most of us who have been following The Irishman are against digitally de-aging the actors for the flashback scenes. I’d much rather they went for casting different actors, a la Once Upon a Time in America. As well as the margin for error being smaller, it would also add a nice dynamic, seeing as though it is probably going to be noticeable when actors who are over 70 years old are going to be playing 30 year old versions of themselves, but when you cast different actors they bring their own little ticks to the role.