I've been running for about thirty years now and things are getting increasingly more difficult. But I'm a firm believer that as you age it's best to follow that old saying "Less is more". I don't mean you should stop running or working out. I think you have to moderate your training by using cross-training to make up for those extra runs that you used to take. I used to run 5 to 6 days a week for a total of 35-45 miles. My body just can't take the wear and tear of that anymore. So I now run 3 to 4 times a week and mix in 1 to 2 mountain bike rides on rail trails. I prefer being out in the woods rather than on the roads competing with traffic. I also would like to mix in some weight lifting 2 times a week, but I haven't been disciplined enough lately.
I also have developed a routine where I run at work during my lunch. We have a small group of runners that run at lunch and two showers in the basement to clean up after. Then I run 5 to 6 miles on either Saturday or Sunday, depending on my schedule. The key for me is to not think too much about it and run early on the weekend before something gets in the way or you get tired.
Happy running and writing