Having strong knees on the trails means a much better chance of sucess and much lower chance of injury.
Being a geezer means you have put a few miles on your knees. Fortunately there a few simple things you can do can help you to continue to use and abuse them with less pain.
I was taught these the first time I tore cartilage in my knees, back in the day. I am not a doctor, but this is so simple and has allowed me to continue to dance, run, pack, climb and bike for the last 21 years.
Lie on your back and extend one leg above you. The other leg can be straight on the ground or bent. However you feel most comfortable.
Relax the knee. Straighten the knee (not hard, this is a small and relatively gentle motion). Repeat for say 15 times.
Rotate the leg out from the hip so that the foot faces off to your side. Repeat the relaxing and straightening of the knee again 15 times.
Rotate the leg IN from the hip (toes are aimed across your body. Repeat.
Do 3-4 reps of this on each leg. Depending on your conditioning and the state of your knees, you may notice that your leg is shaking all over the place. Lower the number of reps.
This helps strengthen and stabilize the laterals around the knee, protecting you (me) from further injuries.