Somebody may have already posted something very similar and I apologize for being repetitive but I haven't had much time lately and couldn't read through all the posts.

The masters athletes that I coach (over 40 yrs) generally get 2 rest days a week and I periodize their schedules such that they do 2 harder weeks and then have a recovery week where time training or mileage goes down to about half of what they did on their hardest week.

Rest days don't have to be total rest days but they need to be easy effort activities, like a very light 30 to 45 min recovery ride or yoga.

I hope that helps.