I'm 80, had a TKR of the right knee 3 years ago. Like you arthritis was the main culprit for the pain. I work, play and enjoy everything about my life on the farm including culling trees, plowing, planting, gardening, welding, etc. Home repair of all kinds are also on the list of tasks I'm needing to accomplish, so I think I qualify as being busy.
I went into surgery with 5 goals:
1. Walk and sit without pain
2. Sleep without pain
3. Walk up stairs without pain
4. Walk down stairs without pain
5. Get down on my knees without pain
Tasks #1, #2 & #3 all were good within the first few days and weeks. Task #5 was a little different because of the lack of feeling in the kneecap and the weird feeling it had I adapted the task by using knee pads. It took months to be able to do task #4 with some degree of success but after a year all tasks except #5 are now well within my wheelhouse. You have to remember that surgery is very hard on us more mature folks, even active ones. When not used even for a few days muscles tend to get soft, blood flow has decreased. I learned that the top portion of your calf muscles act like tiny pumps helping blood get back to the heart, hence keep walking.
During my 12 month checkup I told my doctor about my list of goals and how I was doing with each. He told me the knee replacement was the roughest of all the joint replacement surgeries and to give it time to heal. Today I'm even better with all except #5 and I'm OK with that. We've all heard that old saying "Everyone heals differently", so keep up your spirits, give yourself permission to be a little slower and take each day as they come and go live your life.