Hills I had barely noticed before became mountains. It grew harder to come back from injuries. I raced less often, and then only rarely. These days I cover four miles four times a week. Typically, I run a mile and a half, walk several minutes, run another mile, walk, and finish with a half-mile run.
Every workout is an interval workout.
I could, of course, cover more distance by running more slowly. Stubborn pride keeps me from doing so. Partly it s habit. I was a road runner in the 50s and 60s, when the activity was a happy little secret known only to a few. I ve raised daughters who run, and I hope I have more years left to run with them.