You might want to give your age more than a casual thought. By your pseudonym I infer you actually know quite a bit about training in the competitive athletic sense. From my experience around your age or a little later it is common to fall down another step in athletic performance. So, "training" isn't so much attempting to gain performance seconds as it is keeping what you have and maybe improving satisfaction.

This was brought home to me yesterday when I was doing a stint on the elliptical trainer and, afterward, chatting with some 50 year olds. One has cancer and was supposed to be dead several years ago. By virtue of his attitude and workouts he has slowed his demise. Another has decided that avoiding big injury is The Goal. As has been posted on BF several times, being forced to take time off by over training or by injury brings with it a decrease in performance that cannot be overcome.

So, ride a lot. As many miles as you can comfortably fit in on a daily basis. Don't worry about heart rate. As long as it is beating and you are conscious the heart is good. At all costs avoid the common over training accidents and injuries. At 58 you could recover 95% plus. Maybe even 100% if you are exceptional. At 68 or older you are lucky if you recover 85-90%, no matter how hard you work. In the end no one can tell you exactly what to do other than try to avoid injury or accident and keep at it. At our ages there just isn't a lot of clinical information so each of us is an experiment.

A bit of humor. I was finishing up a ride a couple months ago when a female stopped me and asked to chat. She told me she saw my white hair and assumed I was OLD. I told her I wasn't as old as I hoped to be but that was out of my hands. She said I was a strong rider and asked if I could swim. I answered "yes". "Can you run?" I told her since my spine trauma I couldn't do it very well but was working on it. Then she sprung it on me. "I'm an X-Games coach and you are such a strong biker you should consider competing." Like you will do when you read this I laughed. Still......wonder whether that was a scam or a voice suggesting I change my ways........