Blimey people, can we get off the comparisons roller-coaster? It's obvious that some people can do the Camino in very fast time and are comfortable with it. Others are not. The OP's advice is very sensible - shorter distances until the body is trail fit. What are those distances will vary from person to person.
On my first Camino (unfit, not a great walker, heavy pack) I aimed to start by doing less than 15km a day. That worked for me and over two weeks I became fitter. I was gradually able to walk longer distances without injury but 8 caminos later I still like to keep the kilometres down under 20km per day for the first couple of weeks. That's me.
I sometimes think
Brierley and other guides are a complete menace because they set expectations of "normal" stages. There are no normals! Humanity is infinitely varied.