You can forget how to run.
You think you still remember. Your mind imagines you surging and flowing over the landscape. You remember the exhilaration.
But sit too long and you will forget. You grow heavy and clumsy and your lungs hurt. Short seems far.
But here's the thing ... life ends. Are you ready to stiffen and slow and be sedentary like mud at the bottom of a river?
Everything you want is there before you. There is nothing to do but learn again. Start slow. The flow is still there. Every day it come to you a little more than before. There is time enough to die tomorrow.