I will turn 74 this year and I can really tell that I am slowing down. I have converted to metric hiking. Saying that I hiked 10 K sounds much better than saying I hiked 6 mi. The big advantage of getting older is that it becomes less important to prove things. If I go half as far and half as hard it is OK. Another thing which has changed is that I no longer spend as much time on logistics. Hiking in for 3 days and then turning around and hiking back out on the same trail eliminates car spotting or getting transportation and it is just fine.