"Too long" can even be as little as 15-30 minutes. My job requires me to be on my feet all day but typically I am always walking or moving around, which causes me no pain. However, if I am watching a show or doing something that would require me to stand relatively still for even as little as 15-30 minutes, I get ridiculous pain on my knee joints.
I'm a young guy as well so I feel like this shouldn't be happening. The first time I noticed this was 4-5 years ago when I was 15/16 and doing some landscaping work, where I'd be standing still many times while watering plants.
I don't know if it's genetic, I messed it up doing heavy squats too fast back in the day, or if it's from improper footwear while playing sports or running.
Any advice?