Hell, the top Reddit comment on a recent image of an adult woman sitting on her knees was "my knees and back are killing me just looking at that!" with hundreds of people weighing with their stories of bodily problems and how they can't even jog. Presumably a demographic much younger than what we're talking about.
I remember thinking "wow, we are dying."
"We recruited a random sample of Beijing residents age > or =60 years. Subjects answered questions on joint symptoms, and knee radiographs were obtained. Subjects were also asked to recall the average amount of time spent on squatting each day at youth (25 years or so)."
The full text of the paper is unavailable (404) so I can't say whether they controlled for factors such as family income, occupational history, weight issues etc. Relying on people in their 60s to remember how much they used to squat daily 30+ years ago doesn't seem like it will give necessarily accurate or reliable data (though I also can't think of other methods that don't involve time travel).
I think more studies, with better quality data, are needed to definitively state that prolonged squatting leads to knee issues. And in the Western world, many can't even do a full-depth squat, let alone prolonged squatting, so maybe start with that before worrying about knee issues.
The article buries the fact that "there are studies to suggest that populations that spend excessive time in a deep squat (hours per day), do have a higher incidence of knee and osteoarthritis issues."