I'm 55 and I've hiked the entire series of villages. Personally, I would add this comment to those above: the trails are no steeper than some of the alleys in each of the villages!! There are some steep alleys! I certainly didn't find it any steeper than an easy walk here in Ireland.
One morning when we started out it was pretty chilly - but by noon it was sunny and we needed sunscreen and hats. Since there isn't any place to change along the way (other than someone's house!) be prepared to layer your clothes! (I was there in May).
We also "winged it" and didn't have any place to sleep lined up. We had no problem sitting in the squares and seeing other tourists being greeted by their hosts. Upon approaching a host they each said "I'll come back when I check these people in" and a relaxing coffee break later, the hosts came back to accommodate us!
We also discovered AFTER we hiked it that one trail was closed. "Closed??" we asked? Yes, there were signs saying it was closed. But unfortunately for them, the signs were only posted opposite the direction we were walking so we never saw them. Possibly that was intentional by the locals but I don't know. The trail didn't seem any worse than another. I will add that I wore hiking shoes and was glad to have them. Incredibly I saw some women in fancy sandals - I don't know how they did it!!
One day we took a boat trip to a neighboring village and hiked back, doing that section twice. If you get tired, maybe a boat ride instead of one section walking - the boat ride was wonderful. I highly recommend it!
You'll love staying over. The cafe's on the hillsides are small, quite, have great seafood. At night they are almost empty as the day tourists have all cleared out.
Enjoy!
Susan
American living in Waterville, Ireland