I think the OP's post is an interesting on-going situation. From what I have learned it come down to genetics. Some people just don't tend to get injured. Some people stretch , a lot! And, some people, like myself, stretched and did high mileage, but after 40, tended to get injured.
I have seen almost every scenario. I have seen people in their 60's who are still running strong and often. And, they are still competitive. And yet, I see others who were great runners, who's body broke down and they can barely run 10 miles a week.
So, what's the answer? Stretching? Taking days off? Listening to your body? I am assuming all of these and more.
No matter who I speak to, a doctor, a trainer, a great elite runner, a coach, it all comes down to one common piece of advice. Common sense.
"The problem with common sense, is that it isn't very common" (Ben Franklin)