I walked my first Camino at age 70 (2nd at 71) and very strongly advise you not to use a travel company. I don't think their services are a good value for something that is easily done on your own, but value means different things to different people and we all have different budgets. More importantly, we all have different bodies. I think it is so important to be able to have a shorter day if you need it. I met others in my age group on the Camino and some were struggling to keep up with the schedule their company had made. Also, walking alone you can stay at hotels any time you want to. You can make reservations on booking.com you can use gronze and
wise pilgrim to find accommodations. I would book a few days ahead, no more, and let your body be your guide on how far to go. When you get close to the last 100K you could make more reservations if you feel you want to -- at that point you will be in touch with the distances that work for you.