In my partial meniscectomy they found "1/2 cm area of superficial articular cartilage damage" what does this mean for my knee in activities + health?

Early Arthritis: At the young age of 20, this indicates very early and focal arthritis. The location of the defect (weight bearing or not) is also very important. I would limit load bearing excercises such as jogging. Bike, swim, and do eliptical instead. Supplements such as glucosamine and chondrotin sulfate may help, as well as a visco-elastic injection for cartilage nutrition. Check with your surgeon.