"Well I am in the early stages of treatment, begun with Prednisone about two weeks ago. With a nearly over night recovery, where prior getting out of bed in the morning was a real struggle or just turning over in bed was painful. What possessed my control center to go out of complete control."

I don't know the answers to your questions but I'm at peace with whatever happened. I have read so many theories that it is safe to say that nobody really knows.

Autoimmune disorders can strike at any age so I don't think age explains everything. However, I do think "immune system senescence" has merit.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9261375/
Since PMR/GCA is primarily an age related condition, I think age is a factor for us.

I have another autoimmune condition called "reactive arthritis" which was first diagnosed at the age of 32. This condition derives its name from a reaction to an infection. Clearly age wasn't a factor because I was in my prime.
https://www.mayoclinic.org/diseases-conditions/reactive-arthritis/symptoms-causes/syc-20354838
There are many types of inflammatory arthritis and symptoms overlap with PMR. It is very easy to get misdiagnosed. When I was diagnosed with PMR in addition to reactive arthritis, the pain was the same except perhaps it was more widespread. My response to my rheumatologist when she asked if my muscles or joints hurt was I couldn't differentiate the pain and simply said it hurts everywhere.

A simple explanation that I think explains everything well is summarized with the following:

The body has ways of getting what it needs. I would speculate that PMR is the body's way of saying it needs more cortisol. Cortisol is the "stress hormone" which needs to be produced in response to stress of all types --infections, physical and/or emotional stress are some examples.
https://www.ncbi.nlm.nih.gov/books/NBK534809/
Prednisone is a corticosteroid that supplements the cortisol our body produces. In my way of thinking, PMR is a not so subtle way that the body says "more cortisol please."