Wow, a lot of great answers and inspiring stories! I don't have a huge amount to offer, and I'm a mere 56, but I, too, have had an assortment of physical ailments, arthritic and otherwise, kicking in. I think stretching and moving the various parts of the body are essential to improving blood flow, promoting healing, and compensating for arthritis, as other have suggested. I personally am a fan of yoga, but I came to my senses and started taking what they call "senior restorative yoga". If done correctly, it is much gentler and easy on the body, with all the benefits of yoga still there. None of the potential strains you get from trying to do vigorous yoga with someone 25 yrs younger than you! And for what it's worth, yoga people are nice people, very welcoming, and maybe someone there would like to backpack, too!
And regarding distance: anything that gets you any distance at all from roads and electricity is totally worth it!
Happy trails!