What do you people want, dead ghosts that lie motionless on the ground?

Anakin appears as himself as he should have been by that point in his life. His redemption carries through to the Force-afterlife. When he was redeemed and lay dying in Luke’s arms, he was Anakin again, and Vader was no more. To paste Hayden onto Anakin’s ghost is to truly divorce yourself from the story you told in 1983. That’s the whole point of Anakin’s story in ROTJ: he did NOT die when Vader arose in the pre-ANH era, he is alive and he came through at the end. Anakin’s ghost therefore appears, as do Obi-Wan’s and Yoda’s, at the age he died.
It’s amazing to me how people struggle with the redemption plot of ROTJ, which is my favorite aspect to any of the films. (Though ROTJ isn’t my favorite overall.)