One of my uncles had his first knee replacement when he was 67 yrs. old, the second when he was 68. That was nearly 4 years ago. He deer/turkey hunts, fishes, & has hit every state in the union as of this spring on his Harley. Just as they were taking him to surgery on the last knee, he said he looked up & saw this drop-dead-gorgeous nurse. He said,"Ma'am, can I play tennis after this?" He said she smiled & patted his hand & said "you sure can." He said,"good, ain't never played tennis in my life!" His advice is: get you a good cane, listen to the doc, & work hard. His hunting buddy had a hip replaced a couple of years ago, & does whatever he wants to.
Hang in there. We'll be thinking about you.