Almost all masters distance runners that race competitively, tend to overtrain in terms of volume and undertrain in terms of keeping explosiveness and speed. The runners who have declined the least, are the ones willing to sacrife some volume, so they can get in plyometrics, drills speed work and strength training.
Aa one gets older, recovery becomes a problem. One has to accept that. If one tries to do the same volume and intensity as in our twenties, we are going to get injured or too tired all the time to run well. Unfortunately for most it's the intensity and explosive training that goes.
One has to almost train like the average high schooler, mind you, not the high mileage high schooler. It is perfectly possible to run well on 40 miles a week. Many high schoolers do it all the time with even as little as 25 miles a week. As I have aged, i find that I do not lose aerobic ability as easily as my explosiveness.
One little trick is to really do periodization in earnest, where one runs higher mileage at certain times of the year, but lower mileage with more speed work, drills and strength work, most of the year. But as you workout, always remember that your body does not get better significanlty as you do the work, it's when you rest and recover after the hard work, that the magic happens. Good luck