Welcome Deb! I walked alone in the winter (Jan-Feb) and found it to be a great time to walk. I am a 62 y/o female - not in the best shape. There were Pilgrims on the
Camino Frances so not too many nights alone. The weather is cold and your son would need to be well prepared for snow and ice. It depends on the year. I only had two days of snow and relatively warm weather in Galicia. I found the information on this forum very valuable in preparing me for my walk, especially equipment/packing lists and information on open albergues. I am sure some of the veterans can steer you to the posts. There are also some good blogs from winter walkers and winter walking guides. I don't know how old your son is, but I found in mid-January I ran into a lot of college-aged pilgrims on break from school and several in their early 30s. A lot of them were walking solo but had formed what we call "Camino families" and we're walking together. Hope this helps.