I fell victim to the "getting older" mentality. I've done long back-to-back training runs several times over the last 18+ years of long distance running. I've suffered aches, pains, injuries, crushing fatigue, never ending hunger, illness, mood swings, and burnout. More of these as the years have gone on. I assumed that the slowing down, the aches and pains, fatigue and the rest of it were just the price to be paid if I was going to keep running.