I took this tour a few years ago, when I was in my mid-70s. I was walking and biking quite a bit, and running a bit. Good balance and eyesight.
As I recall, you will walk a lot, sometimes on uneven surfaces: paths, cobblestones, etc. in many places, especially in Cappadocia. Also clambering through some narrow passages in cave homes. But I don't recall feeling that a lot of endurance was required.
I don't think age matters, per se, if one has at least average-for-that-age eyesight and balance, are used to walking several miles a day, and have confidence and a sense of adventure.
This tour, along with the Greece tour, was my favorite of the 8 or so that I have taken. Much different from western Europe. Tremendous sense of history, multiple civilizations. Great food, too. If you have taken other RS tours, you know the drill. Just put this at the active end of that spectrum. I'd go again in a heartbeat.