I am 63, 6-3, 250 (should be 225). I usually carry 20-30 lbs of gear. I hunt mountains and canyons of AZ where terrain can be very rugged and steeply vertical most of the time (typically up one ridge, glass, then next ridge, glass, etc. then all the way back to truck at the end). I have sports injuries on both knees (both medial collateral ligaments severed in left knee in late 20's, and an ACL severed (patella tendon replacement) and 30% cartilage loss in right knee in mid 30's.) I continued playing ball until mid 40's, but not as aggressively or as well as when I was younger, and still play tennis. Was told by physicians at time of surgery that I would have arthritis by the time I was 40 and be candidate for early knee replacement, especially in right knee. Started taking triple strength glucosamine chondroitin daily since age 40, Golden Milk daily since age 58, and extra strength ibuprofen (800mg) on days of heavy exertion. During heavy hunting days in rugged country, I wear neoprene knee wraps ( I prefer the Walgreens generic copper fits. ) and have recently started using 2 trekking poles regardless of load weight carried. I have a sedentary job and do no special exercises or regular workouts (although I should).
I still DO NOT have arthritis in either knee, thank God, and hunt anywhere I want, regardless of terrain, often miles from the truck, tens of miles from the nearest paved road.
I heartily recommend all of the above. Believe me, if I could drop doing any of them, I would. All are necessary for me, but they have kept me going with people half my age. No complaints.