I did a bit of bike touring at your age, more or less without training or preparation, and I was (and am) by no means athletic. What I found, empirically, was 70/day was the most realistic goal, with a fully-loaded touring bike. If we went further one day, we wound up not going as far on the next. We also found it was far easier to break it up into an early morning ride and a late afternoon ride, avoiding the heat and peak UV.