Just a note about the utility of pre-training for a Camino, and honestly evaluating personal fitness. A particularly memorable time on one of my Pilgrimages was a time I and my son Caleb departed from St Jean Pied de Port.
After a short refreshment break at Orison, my son and I were about a kilometer up the road when we came upon two young women stopped alongside. One was crumped and sitting, sobbing, while her friend was standing and looking a bit helpless. We stopped and I knelt next to the crying woman asking if she were injured.
Her reply was in heavily accented English broken up between sobs, "Why do people say just anyone can do this?" I patted her shoulder and asked her friend what happened.
She said that they were both not fit for this kind of walking and began struggling when a ways out of St Jean. They had managed to make it to Orisson and had rested a while and were not sure if they should continue. A few other pilgrims told them that the rest of the way was not as hard from Orisson, so the two young women decided to keep going.
Obviously, they didn't make it very far before one had reached a limit. I asked them if they knew whether or not they wanted to continue or if they wanted to return to St Jean. The woman who was sitting was quick to say that she was done. I asked if they wanted to have Caleb and I help them back to Orrison to see if transport back to St Jean could be arranged, to which a grateful "yes" was given.
Caleb stayed with our backpacks, and I took the pack (gads, it was heavy) from the crying woman. Her friend carried hers and we started down to Orrison. Along the way, I told them to rest for the night before deciding to give up their pilgrimage. I explained that it was fine if they wanted to taxi or bus to Roncesvalles and start from there, but to get a good night's rest before deciding anything.
After we reached Orrison, the friend was able to talk to one of the staff there, so I left.
I have never started a season of wilderness backpacking or a Camino without a decent level of pre-training. How much pre-training? To a level where I know that I can enjoy my first steps of an anticipated hiking trip or Camino. That does not mean being in ultra-fit shape, but it does mean that I want to be able to enjoy my time walking from the very beginning, and be in a mental fog of huffing and puffing. . . . I want to enjoy the sights and sounds externally from myself, not having my mind focused on how miserable I feel.
YMMV.