Okay, it is officially 4 weeks since Grandma's Marathon. My running has truly suffered for that time a lot of it, just getting the joints (and energy) back to attempt running, let alone, racing again.
I know I am older than most, younger than some, of the other runners, but the recovery time has always seemed to fit one formula. One day for every mile raced. 26.2 miles, 28 days of rest.
This formula has stood the test of time from my 30s to 40s to 50s. Sure, I have run two marathons within 28 days of each other, but neither one of them were a PR. I think you probably have 4 good races that you can gear for each year. More if you are only doing 5K, less if you are only doing marathons. If I had to put my finger on it, I'd say that 5% of all the miles I've run are racing. The rest are training for the race – either a long run, a tempo run, speed workout – or just the enjoyment of running.
I enjoy the time off after a race like the marathon. You can catch up on any activities you've been neglecting (work), skip workouts you can't miss or just spend 4 days not running and canoeing/hiking with your wife in the BWCA (Boundary Waters Canoe Area). It's a rebuilding time that allows your body/muscles to get back to the point of wanting to strive for a new goal while allowing your mind to forget just how brutal that last race was.
I think this is what nature intended. Stress/Restore/Replenish. What's my next goal?