My knee hurts....

I'm still in my 30s, but maybe because I've been squatting since I was young, my knees hurt too much when I do lower body exercises during workouts these days. Today, I thought I couldn't exercise because of a sharp pain in the morning, but after a while, the pain subsided, though I'm still worried. Sometimes I feel like my knees are slipping backward. Has my knee cartilage already worn out?