Biking is a great way to get exercise without pounding on the knees, and I'm glad you found it. I was an avid runner in my 20s thru my 40s, and I had biked off and on. While I'll never run longer distances again, I leaned into mountain biking the past year and took my longest ride ever: 60 miles on my 60th birthday. It only hurts when I fall. :) I wrote about it here: https://robertroybritt.medium.com/can-i-really-mountain-bike-60-miles-at-age-60-915a8571de09