I started running back in 1981, and ran 5+ miles a day, every day. Ran several 10k's in those years. Backed off a lot after a while for some now forgotten reason, but never quit completely
I've run a couple of 5k's in recent years, and have maintained 2-3 miles 2-3 times a week, mixed in with weight training at the gym and kayaking out on the lake once a week.
Last June I really messed up my knee (and shoulder), and just recently started jogging a couple of miles once in a while. It still hurts and I always wear a brace when I run or work out. Makes me mad; at my age (58) my legs were the strongest part of my body and never hurt no matter what I did.
At the start of the year, I set a goal to get back to 5 miles runs again. Hope to get there maybe next year.