Age does make a difference. There is a limit to how much wisdom will get you through the purely physical challenges that a long distance hiking trail record attempt presents.
I am sure that David will be the oldest record holder (with support) of the PCT (55 y.o) and that he will be the oldest record holder of one who has covered 330 miles of the Colorado Trail in only 6 days (59 y.o).
My physical abilities have started to diminish since the age of 53 due to a slightly decreased lung capacity and being overweight. Structurally I'm still fine. My 50-60+ mile days are a thing of the past. I still might have a few 40+ mile days left. I'm still capable of 30+ mile days when needed with a little night hiking involved. These preceding statements involve mostly day hiking with vehicular support. David and I are only two weeks apart in age.
He is a runner and I am a walker.
Great effort and I hoped he would make it. Never go wrong by setting goals and training for them even if they do not work out. You are still farther along than you would of been.