1. We are looking at what, 20 years between end of EP3 and the end of EP6, when Vader is finally unmasked. People change in 20 years.
2. Anakin suffers from some agonizing injuries. We do not know to what extent is body needs to be rebuilt. I think its a forgone conclusion that his hair never grows back. If facial reconstruction is needed, that kind of thing would contribute as well.
3. As for the ghost issue...did Yoda or Obi-wan come back young (well, the younger Obiwan might still get pasted in for all we know)??
No.
Why shouldn't the old Anakin appear?