hi,
thank-you for providing the brief history of you.
As you mentioned you are getting
fatigue and there is change in your blood pressure, Pulse and you don't have any other issue.
As to understand here, that you been riding alot for almost 100-s of miles your body will ofcourse get tired.
Since now you are 80, you should understand one simple thing here is the ageing process. So long years you have kept yourself with good health and steady flow. But now ageing is something which is slowly coming towards you. You need to focus on doing regular
meditation, breathing exercises and strength conditioning. As the ageing progress there is a chance that the
metabolism in the cellular stage needs attention. And ageing can be fought by taking proper diet, sleep, rest, exercises, meditation etc. I am sure when you have passed 80 years like a rock you can still move further lkke a rock. for time being break your 100 miles in short distance and then take a next step. It will surely help you.
I have been seeing 90+ people and the combination of meditation, exercises, diet, breathing exercises, etc have made a wide lot of differece.
I hope to see you soon with the rocking style again.
regards