I have been reading this forum daily for about a year now, but rarely post because I don't have a date fixed yet for my camino. However, my interest is strong. I will soon be 60, and plan to do a fairly short camino first, perhaps from Porto to Santiago. I would love to do El Camino de la Plata, but don't know if that will ever happen, except in my imagination.
For a couple of months now, I have been walking about 60 km per week. That doesn't approach what I will need to do on El Camino. However, I wanted to check gradually if my aging body was up to it, and also since I work full time it is hard to find the time to walk more. So far, I'm happy with the results. I have had no problems with my formerly-injured knee, and I feel generally "stronger". Now I scarcely notice a 10 km walk.
When I have a date fixed for Spain, I would hope to train for a couple of months and increase my walking to about double. As you, one wants to become fitter without wearing out!
Meanwhile, I continue with a modest pace, and thoroughly enjoy reading about everyone else's training, pilgrimages, equipment planning, and memories.