I've run 9 full marathons, a bunch of 30K,and Half Marathons back in the 80's. I used to train 55-60 miles per week.
Best marathon time was 2 Hrs, 53 minutes, 20 seconds, or 6:17 per mile at the Track Capitol Marathon in Eugene, Oregon in 1982. I ran a half Marathon in 1Hr 11 minutes and change or 5:56/mile around that same time frame.
One of these days I need to get off my azz and get back into shape.