A lot of miles repeated over consecutive days can be tough. I've hiked for a month at a time and biked for years. If the first-day distance is a "stretch" distance for you , i.e. you've only ridden up to a max of that distance, then you might be setting up for a hard time. Butt, back, shoulders, neck, wrists, hands, quads, hamstrings--almost any weak link in your body can be exposed, and that's just the musculoskeletal parts. Fatigue from age, lack of fitness, and past illness/treatments can flare up as well.
A lot of people your age do ride longer distances like this and enjoy the time, but if you're not adequately prepared physically, you are not likely to end up with the good, positive tiredness at the end of a long but fun ride with a friend. You're looking at a butt-whooping endurance ride with pain and fatigue that can leave you calling for a pick-up on the third morning.
With that said, you might have time to prepare if you start now. Keep posting your progress here and ride as often as you can, even if for short distances to the grocery store. You're only going to get stronger. If this ride doesn't work out for you, another one down the road likely will. Consistency and increased distance will also bring any of your physical weaknesses to your attention.