There is nothing wrong with my belly button or my nipples. My legs though need work. Did 8 sets of 20 bodyweight squats. 7 sets of 30 seated calf raises. And 5 sets of 25 seated legs extensions today was tired so will do hams later this week. My lower body was ignored and injured for a long time. Legs are where I plan to make the most gains.
Good work on quad workout. I assume you are doing high reps as you need to keep the resistance light because of your knee issues. Otherwise, I'd suggest fewer reps with some resistance depending on what equipment you have available. Since I have been doing them at home where I don't have leg extension equipment available, I also do 5 sets of 25 reps. I think this will keep each of us toned, but it probably won't build much muscle.
Honestly, your quads look good but obviously not huge. You've mentioned that your knee joints are compromised. Bad knees are a hindrance to developing full muscular quads. This is such a bitch because I've noticed that the older I get, the less muscular my legs are. I think for people with compromised knee joints, leg presses are preferable to squats....at least that's what my physical therapist thinks.
When I was a teenager, I took my horse out for a couple of hours ride everyday after school. Although I was ridiculously skinny, my legs were in great shape. Now that I am an old man who spends far too much time sitting around not using them, my leg muscles have atrophied. Unfortunately this is not uncommon among old men like me. So, keep doing whatever you can to keep your legs as strong as possible. Steve Reeves once said he had well developed calves because when he was a kid he had a paper route in a hilly neighborhood. He wasn't giving enough credit to his good genetics.
Sorry I teased you about your nipples awhile back....Honestly, I was just kidding you. Since you mentioned it, your navel is fine. Everyone's navel is unique. Mine has a 2" scar above it as a result of the robotic prostatectomy. Before the surgery, I had a really decent looking navel. I once knew someone who had no visible belly button. It was weird...like he was an alien. LOL. Can't remember what caused it now, decades later. (I know, you think I am weird because I notice stuff like that). Just don't take it personally.