I'm 54 and been running since I was 27 ish. Started "late" in that regard compared to most seasoned runners. Most would say I'm barely a runner since I do three days a week at 3miles, 4miles, 5miles so 12M a week unless training.
Used to do 3-4 races a year including half marathon. I've found once I ramp my miles up when training more injuries were happening. I just did one race last year.
As hard as it is on the body I have not found a cardio that comes close in regards to results and efficiency (how much time it takes, great workout). I've tried biking, spin classes and swimming laps. Yes, at some point I will have to give it up but I'm not looking forward to that day.
One thing I do different from most is my pacing. I might be a bit faster than a jogger but am not a "racer". A 3M run I shoot for a 7:20 pace if I'm feeling good. 4M pace is 7:30, 5M 7:40. I have to be feeling real good to meet those goals however. If it's hilly, hot, or I'm just not feeling it (which is 50% of the time) I can end up in the 7:50-8:00 pace very easily.
What has helped my body the most especially how back is squeezing in a Yoga class once a week.
My last half M was a 1:38 in 2013 so I'm not getting awards that is for certain. I never ran cross country so I don't know what is feels like to run a 6:00pace
I'm not in that half M form right now but would like to get back there soon. Maybe if I ER--- Ha.