All senior citizens, except for one. O.K.
You might want to not go to the Udo Shrine. Here is a link:https://www.tripadvisor.com/ShowUserReviews-g1023424-d1238711-r1929291...
I remember a lot of steps. I also remember a tunnel that I didn't see until I had walked up and over the top of the hill. It will cut down of some of the steps, but not all. This link to a visit has an image of the map:http://jprail.com/destinations/kyushu-area/my-trip-to-udo-jingu-shrine...
It looks like that there is a "long way" around that will not have that many steps. I don't remember this even being a option when I went. I never picked up a map, and I probably should have.
As for Takachiho, I don't think that is a train station anymore, just a bus depot. I stayed at the Hana Ryokan Iwatoya, which is close to the Amano-Iwato Shrine (The shrine that has the cave that the sun goddess Amaterasu hid herself in. The Ryokan had one of the best meals I have ever had in Japan. I only stayed one night, and if I ever plan to go back, I would stay here again for 2-3 nights.
The Ryokan has a shuttle bus, that will pick you up at the bus depot. I ended up arriving mid morning, putting my luggage in a locker at the bus depot, and waking to the main shrine and seeing the gorge until mid afternoon. When I got back to the bus depot, I grabbed my luggage and took the regular bus to the Ryokan. I knew that the Ryokan had a shuttle bus, but I didn't think to call and have them pick me up.
Another interesting find in Takachiho was a center near the bus depot which was doing make-and-take crafts. I was there a few days before Golden Week, and the craft was to carve a Magnatama out of a soft stone like Onyx, and make a necklace by threading a leather cord through the eye of the Magnatama. I was running out of time, and didn't stay and carve my own.
I hope this additional information helps.