I recommend that you take 1-2 weeks off after a formal training plan is complete. We call this a recovery “firewall.” It helps ensure your body can recover enough in order to repeat the training cycle indefinitely. Those 1-2 weeks should include very little running, with no running at all totally acceptable, and perhaps just 2-4 hours a week of total exercise.
When that 1-2 weeks is complete, then you are free to begin a new formal plan again. Repeat that cycle for the next…oh…40 years and you’ll be able to train and race indefinitely.