You could get John Hurt to play Old Eight instead of McGann to show that he stayed in that form for a loooooong time.
There are several problems with saying that Hurt is an aged McGann.
For one thing, the dialogue indicates that Clara saw McGann's face, yet she doesn't recognize Hurt's face, which makes it unlikely that Hurt=aged McGann.
The dialogue also seems to indicates that, because he "broke the promise," that whole incarnation was tainted. Whatever good that Doctor may have done, what that Doctor "did without choice, in the name of peace and sanity" overshadows the good. If the Doctor thought of his McGann incarnation in that way, would he have shown it to Craig? Would John Smith have doodled it in the Journal of Impossible Things