For the record, I'm 55 now.
Lot's of good stuff above and I agree with the common threads...
- Injuries happen more easily and take longer to get over.
- Harder to keep weight under control.
- Feel like an old cripple at the beginning of almost every run, but get warmed up within a few minutes and everything feels fine.
- I started to notice the injury / recovery impacts in my late 30s.
The things that stand out most for me personally are...
- Almost every morning when I get out of bed (especially after a hard run the day before) I'm so stiff that I start thinking "I'm going to have to take today off. No way I can run with my legs/back/feet feeling like this." Then, after I've been up and around for awhile, I usually feel OK and am looking forward to my run.
- On faster (tempo/race) days, I feel like I'm running just as fast as I ever did. My posture and turnover feel good. I can get into a good rhythm and can push myself when it gets hard. But, as others have stated, the clock does not agree with my perception.
- From age 51 to 53, my training and racing were going very well. I was averaging over 60 mpw for much of that time and handling it OK. Then I got bad PF in both feet and last year was an on again off again struggle. My yearly mileage was less than half the previous year and I gained a bunch of weight. I've been pretty consistently rebuilding since early this year. I've dropped about half the weight I gained and seem to have plateaued. I've been averaging low 50s mpw for the past few months and just can't seem to push any higher. I haven't raced much, but my times are way off where I was 2 years ago, despite feeling like my training is going pretty well.
- Even though lifetime PRs are ancient history, I find that during periods where my fitness is good, my Age Graded times are still pretty much in line with my PRs from my late 20s and early 30s. So, it seems that my decline is pretty much "normal".