I'm 58 and still do squats. I keep the reps in the 12-15 range and don't go above 315. Still do good mornings, deadlifts, romanians, and cleans. I find my back and core are stronger for doing them. In my 40's I quit the above and did hacks and leg presses along with the leg machines and had back problems. When I added back squats my back got better. Of course I focus on perfect form, low and slow, proper foot placement, wear a belt, etc. My back journey taught me that limiting back movements caused more problems. Actually having a kid taught me that. My back was at its worst when my son was born and I feared what all the bending and lifting a kid would do.....and it cured my back. More than ever it reminded me that core is everything and the platform for all the upper body muscle groups we like to focus on. Stronger core means bigger biceps to me, as heavy bicep work requires a strong and stable lower back. Back problems made it hard to work biceps properly so I am happier than I have ever been with my workouts having added in all the tough lower back exercises. And can't say enough about planks.....3 mins with a 45 on my back. Seriously hope this helps someone. I struggled with back problems for 15 years and even decided to have surgery at one point, but the simplest message I have is that every time I limited myself on back, range of motion, etc I made my back weaker and problematic. I think you have to do it all in a safe, slowly progressing manner and build back your capabilities. And I'm certainly not promoting stupid ego shit we did in the gym in our 20's, just your own safe pace.