I don't know your circumstances exactly, but at the casual 'park run' races that I attend every Saturday, there are many people in the 50 and 60+ age group who actually beat me.

I also saw an age group distribution of marathon times which showed only a slight dip in performance based on age.

The total distance isn't as important as the consistency and dedication to getting it done. Even if it is something like 1 mile, it is the small changes that add up over time making most difference.

I think you could probably run a 5k in under an hour, and spending an hour or so each day doing something to extend the quality and hopefully length of our lives is worth it right?