Training question...

However much rest allows for your body to make adoptions to the stresses you put on the body in training without compromising the length of the program where you cannot get a good build in.

At your age recovery becomes far more important as you recover slower. I would suggest 48-72 hours of rest between your key sessions, or at lest 2 nights of sleep. Adding in more rest days is good but do have a rest day the day before your key sessions, usually people come out a bit flat on the day after rest days.

I know a lot of people advocate the 3 on 1 off method or use a 7-day week for training. Frankly, I don't think that is the best method. At your age I would say to builds of 10-17 days on and 3-5 days off. That is enough time to get in a good chunk of training but not overreach too far and allow for ample recovery time. Within those 10-17 days I would take 1-2 days off, or have very easy light sessions in between your key sessions. Also something I would recommend is a good strength program for the off days. A good program specific to help running, not just benching and squatting. But a program aimed to build strength in the posterior chain, open your hip flexors, and core strength. Doing a strength program will allow you to get more out of your training and train better when you are.

I had a coach do similar to what you suggest with a10 day cycle. It made me feel even more tired. My body like consistent in training with gradual build in training stress. I actually do best to have similar training week to week with gradual build in volumne or intensity depending what part of b my build i am in. I was surprised how constistent training was better for me and less fatigue than with many more rest days. I think the 10 day cycle was more than my body could handle at that time. I was 48 to 50 when consistent training with slow build worked well for me.

Train with sustainability built into the program.

Agree with the above. I prefer to have "big days" separated by rest (rest for me = swimimng and weights, maybe a 4 mile run or something), rather than pushing a plan that takes me to the limit every day. For instance a strong 40 mile bike, 7 mile run one day, followed by a 2000 m swim, 2 mile treadmill and then weight room the next. The swim and weights seem to take off the strain of the "long" sessions. Plus I use an electro stimulator and compression boots if necessary.