Ech. That's pretty shit. I think the entire male part of my dad's half of the family have damaged knees. My dad dislocated his knee 3 times as a teenager. Mine aren't that bad, but they ache for days after I do any kind of running around. I feel your pain, slightly.
That is worrying. Are you overly flexible? Do you do gymnastics? Do you LOVE swimming but can't put your finger on why? Do you think sitting still is uncomfortable/painful? Do you feel better after exercising? Do you have a high pain tolerance? Do you easily shrug of injuries? Because if it is seek help. I'm serious. (Or start stretching and wear "supportive" things.)
Er, in order: No. No. Yes, swimming is fun. No, sitting doesn't hurt. I feel good right after I exercise, but when I cool down my knees start to hurt. I'd say my tolerance of pain isn't high or low. Not really. At any rate, I've been trying to become more flexible. I figured out how to do a proper squat without wrecking my knees, anyway. And a knee brace is probably going to be in my future, I just haven't needed it yet. I think.
Sounds okay.