I ran many of my lifetime PRs after 30, but off of moderate mileage. Then I did try backing off twice (at 35 and 43) and both times ended up with long-term injuries that took years to recover from. At 46 I finally got healthy and as I built up to 45-60 minutes a day realized that I really enjoyed running and that I would like to keep at it for as long as I can. And for the next 15 years I hardly slowed down. The training and racing have been fun, and give some degree of focus, and I have been able to travel to events and sometimes pay for the trip or part of it. It's what I do and what others may think does not really matter.