I had my right knee replaced about a decade ago (old basketball injury). It's not that I'm all that old - in the general pre-op orientation meeting, I think I was the youngest one there by about 25 years!
And I'm very thankful for my new knee, but running is not much of an option unless I want to get that done again if I wear it down. But I can sure walk! I take our 11 year old chocolate lab out at least 5 days a week for a 3-4 mile adventure around our neighborhood, looking for men with beards and hats (ever seen "Sad Dog Diaries"? Hilarious!).
And I just use my good ole Fitbit, and it will map our walkies. I really like the feedback I get on my resting heart rate - down to 57 for the first time a few days ago. I'll take that.
Congrats! That's a great way to stay active. Running is actually pretty rough on your body but at least it's active.