LR Comments are funny. The young folks act like their running prowess is a given and it will last forever. Lots of others are much more realistic. Age slows you down, so does a job, family, etc. But talent never goes away. Those that were very good usually can get back to the top of their age group, whatever age they are. Those that don't have much talent will always struggle to run "fast".
I ran in college and would have thought someone touting a sub 6 was a joke. Looking back, I was nothing special since I ran about 85% of the world record in most distances. Now I am in my late 40s and run in the 80s on the Age Grade Percent. Lots of sub 6 miles still, but it won't last and I know it. I know guys who were national/world class 20+ years ago and they can still dominate and others who could not run 800m with me in a 5k now.
Each injury after your late 30s will kick you down a notch and you will likely never get it back. It is a reality. There is also a reality that a sub 6 mile is still something only a very small percentage of people can do, even within the masses of people who consider themselves runners. Just look at the results of any road race, even very competetive ones. It is a single digit percentage of runners even completeing a sub 20min 5k. The people running on HS and college teams are usually wild outliers from the general poplulation, even if they are "nothing special" like I was and am.