Hello again
Those are great 5K time in your 40s and 50s!
All runners age at a different rate. I once read that most runners have a twenty year window in which to see improvements either as a younger runner or as an older runner.
I peaked as a master at age 47 with Masters PRs of 15:07 (5K), 32:12 (10K), 1:07:30 (half), 2:27:04 (marathon).
My times fell off quickly after that, though I held it together with lots of duck tape for another 10 years, with the wheels completely falling off at age 60.
When I retired from "racing" to recreational running, my body didn't adjust well to running slower, my efficiency and form went to pot and I started to get injuries continuously, making it finally not to much fun to run anymore. I swallowed hard and hung it up a year ago at age 65 deciding I didn't want to be a cripple at age 70 and still be able to enjoy the things I enjoy.
Now I just walk (with occoasional jogging sometimes thinking hey, I can still do this thing!...nah), lift weights and ride an elliptical.
Enjoy the journey my friend, enjoy it while you still can, and embrace your aging process.
Know when to hold 'em and know when to fold 'em!