I'm 48 and having knee problems too. It started a couple of months ago after a run on mountain trails that were pretty icy. I haven't been able to squat heavy (for me) ever since. Even deadlifts cause pain.
I have an appointment with sports therapist next week.
I'll start taking fish oil...
I've been doing dls as long as i can remember. Great for mass. I love the pump i get in legs, glutes, back and forearms.
Like all exercises, form has to be right and can't round your back, ever