Age brings physical declines and that is unavoidable. Once you hit your mid 40's and beyond, you need to make adjustments. Those are:
1. Stop racing your younger self - there's no going back
2. Be open to new ideas about training - your body and mind need more rest than before. Consider replacing some easy/junk/recovery mileage with cross training that reduces pounding. Your heart doesn't know the difference but, your joints will thank you. Also take up strength training, yoga, etc. as this will make your body function better and set you up for healthier golden years.
3. Eat better food and hydrate more
4. Shelve your ego - this works hand-in-hand with point #2. The biggest mistake that I see most masters make is to pull out the old training logs and try to replicate their training from 20 years ago. Worse? They buy a book and then skip to the "Advanced Runner" training plan because they still see themselves as such.
5. Accept your age - you are still going to beat a lot of younger runners but, stop trying to race guys half your age just to prove something to yourself or to impress others. Use the age grading tables to draw comparisons (see point #1) or just work to dominate your age group.
6. Run soft surfaces as much as possible - better for your body, makes you stronger overall
7. Stop overthinking your training - in a perfect world, you can run 12-14 varied sessions, take daily naps, get massages, and spend six hours in the weight room each week. Most of us have work, family, and volunteer obligations at our advanced age and cannot train like college kids and pros. The problem is that we try to train like them and stress out over how to get the volume, the "sub maximal CV hill tempo progression lactate fartlek" work, etc. in each week. Keep it simple! Find some good sessions that work for you that you enjoy doing and do those consistently. I see a lot of older guys getting hurt trying to do the latest marginal gain stuff they read about rather than improving with time honored methods. Look at guys like Tommy Hughes, Gene Dykes, or the late Ed Whitlock. Simple and consistent training makes (made) them successful and not changing their training scheme every month because of some Podium Runner article about the latest lab rat study or LRC thread about what Tinman is pushing this week.