For me it would depend greatly on the tour. Things like difficulty of terrain and distance between services factor heavily. Also at age 69 I am slowing down a bit. That said I might still do long days. I generally wouldn't be doing really long ones in the early days of a tour though. I figure that taking it a little easy for the first 10 days to 2 weeks is a good idea on long tours. Starting out with high mileage and decreasing it ending in injury is a sign of a poor daily mileage strategy. For me average mileage for a tour might be 50, 60, or 80 miles per day including all days, even any zero days unless the trip has a planned gap to spend a week off somewhere or something. I still might do some 100+ mile days at my age, but after some time getting road hardened. I think my longest day on tour was 142 miles and included one mountain pass.