Really interesting topic & seems like some great experiences shared in the 50+ thread.
My ponderings: guess it’s inevitable that the absolute limits of physiology decrease with age, but perhaps there some workarounds
If your previous PBs are soft enough for some reason, you can find new ways to improve. Eg. For me, my half marathon PB of 1h22 was set aged 33. Aged 45 and again aged 46 I knocked out 1h24s, and once am again training with this sort of range in mind. I dunno if I’ll get close to that PB aged 48, but I’ll give it a shot & hope to get under 1h25. The difference is that these days I train more consistently, have less life stress now the kids are older & work is more established, have a regular training partner and a club, have new toys like Strava, treadmill, training peaks/ runalyze etc & am always looking for new stuff to try. Oh yeah, and special shoes .
At some point I guess a biological limit is hit, although I bet most of us never get near it for perfectly good reasons. And actually I suspect it’s not normal or even always very healthy to hit those limits. So while beyond a point there may be no more absolute PBs, age graded PBs are always out there aging at the same rate we do. I have seen run performances creep slowly up from about 70% age graded to almost 80% age graded over the last 15 years & this feels pretty motivational.
At the end of the day we are not pros, winning races doesn’t pay for our lunch, and just being healthy and fit enough to be able to get out there and knock out a 20 minute 5km aged 50 (or whatever) should feel like a pretty sweet thing I reckon. Times and PBs/ age gradings are just one facet of the game