I read an article about 11 things to look for that are signs of aging. One of the eleven was about sagging knees and this is what they had to say about them as a remedy.
At home: Soothe dry skin with moisturizer containing ammonium lactate or urea—both help moisture get through the skin barrier. Take the focus off wrinkly knees by giving your legs an allover glow with tinted body moisturizer. And exfoliate elbows with your favorite cream or brush.
At the doc's: You could consider a knee lift like Demi Moore famously had done. But here's a better idea: Sign up for a yoga class. Poses that strengthen the quadriceps (e.g., Chair, Warrior I, and Warrior II) support and strengthen the knee joints, and also tighten the surrounding skin and muscle. What a HUGE TESTIMONY !!!!!!! Till next time ! Namaste