Kellyro, I've found doctors to be very unknowledgeable about the specifics of nutrition and exercise. I have utilized for doctors for health concerns (after the fact), but for prevention... I've had no luck. My dad ran into the same problem, and frustrated, he asked... "how much of your schooling covers nutrition and exercise?" The answer... 2 hours on nutrition and zero for exercise. I was shocked! No wonder my dad has to use Google to find out how to feed himself (he's diabetic). I haven't been able to afford insurance since they did that government thing that raised the prices and the deductibles (my at-home job doesn't offer it), so I rarely go to a doctor and have to be preventative. I ask my son's doctors all the time about these topics and I end up with vague answers like "exercise is good for you" or "eating healthy is important". lol I once mentioned to a doctor that I ate "clean" (no chemicals in my food) and she thought I'd become a vegan! lol Another doctor thought the same thing when I mentioned "plant-based" diet - said I didn't weigh enough to be on a diet and that vegetarians and vegans are unhealthy (which not only is that NOT what plant-based means, but I have friends that are vegan/vegetarian and they are incredibly healthy - 1 still swing dances in her 80s!). My chiropractor was much more knowledgeable than the dozens of doctors my son and I have dealt with over the years, but I can no longer afford a chiropractor... so, I rely on good form, accurate and thorough research, and listening to my body. I had a 2 year break from exercise, but I'm not new to it - just getting back into something I've loved doing my entire life - being fit.

I love learning more about it, and I've been "out of the loop" for awhile, so I'm trying to play "catch up". I know Cathe keeps up on it - that's probably one of the many reasons that she's been my favorite instructor for decades.
This is a very interesting topic. I don't think the blanket statement of "shouldn't do a move after age _____" is appropriate. Too many other factors need to be considered. Plus, I think many of the moves can be greatly beneficial if modified to the individual. As always, one size does not fit all.
On the subject of deadlifts & squats, the deadlift seems to come very easily to me, even with my low back issues. I am 62 now & I have no problem doing them with weight, but I won't go over 40 lbs. As for squats, I love them. They've been a big help in stabilizing my knees & getting rid of knee pain. I won't go heavy for faster tempo though.
I am careful & listen to my body. Since my shoulder replacement, I do very conservative upper body workouts. I can feel it if I'm going too heavy. And I am not able to use a barbell on my shoulders for anything so I modify.
Since restarting Cathe workouts, I've gained so much stamina & strength back. I love her workouts, variety, & detailed instruction. I always follow her advice to go light or use no weight until I have the mechanics of a move down.
I have to admit, I rarely go to doctors anymore either except to keep from getting dropped as a patient & having no doc if I do need one. I had chronic pancreatitis for many years, & followed all of their instructions & diets & just continually got worse. About 10 years ago, I started my own research, quit the meds, & made huge changes in my diet, totally opposite of what they had me eating. Once I did that, I improved, & have not had anymore pancreas problems. I have a healthy weight, more energy, less pain, on zero pharmaceuticals (Rx or over the counter), no more depression or anxiety, my lab tests 6 months ago were excellent, the list is endless. I'm not criticizing my past docs, I truly believe they were doing their best. But I agree with you that so many of them are not knowledgeable in actual health care. All they've been taught is to prescribe meds & do procedures to manage symptoms. I worked in the medical field as a nurse for many years & that's also how I was trained, so I understand. But for the past decade, I don't go with the mainstream anymore & I am doing better in my 60's than when I was in my 40's.