I started my serious touring when I was in my 40's and would train for a few weeks before leaving.
I always wished to go as far and to see as much as I could in the few weeks I could get off work.
I would start at dawn, ride for 1 to 1 1/2 hrs, take a 15-20 min break, and continue this most of the day
depending where I wished to stop for the night that was interesting enough to casually check out.
This worked out to an 85 miles a day average. As the next several tours came and went, that average
dropped down to 75, keeping in mind that some days I only went about 40, while others were well over 100.
It all depended on the hills, headwinds or tailwinds (I love strong tailwinds) and the interesting sights I
chanced upon. Now at my advanced age, I would plan for 50-60 and no more. My knees and Achilles heals
are my gauge to which I determine how hard I push and how far I go per day.