Currently in my early 30s. Ran in HS, college, and at a sub-elite level (close to qualifying for national championships/olympic trials on the track) for a couple years after college.
I am still in pretty good shape, but because I reached such a high level on the track, I understand that I will never be able to PR on the track again, unless I take up sprinting. I have found new ways to challenge myself - moving up to the marathon, as well as trying to gradually improve/compete for the win in the popular annual road race in my city.
I recently set a road 5K PR, though it is way slower than my track 5000 PR and more of a testament to the fact that I only ran a handful of road 5Ks when I was at that sub-elite level, all as sort of training runs/prize money grabs. But a PR's a PR, and because training has been going well, I think I could set another one in the same race next year.
I think I have adapted well to longer-distance training, and should be able to continue to chip away at Half/Full Marathon PR's for many years to come.