I hiked the PCT in 2006--when I was 53------it is certainly possible to do those miles once you are in shape-----we averaged around 20 in areas w/o big mountains. Also note there seems to be alot of new math that goes on with thru hikers that comes from the attitude that huge miles are somehow desirable.
I have to laugh but there was this group of young folks I saw on the second day and then again in Ashland--and they would go on and on about these huge miles but there they were at the same place at the same time----

If I did this again I would not push hard---I would just spend the summer on the trial and be good with wherver I managed to get---after all no one cares where you get