It's not that unusual for people to pick up e.g. powerlifting past 50 and still get to levels well beyond what most younger adults can lift.
I'm 51, and recently back into powerlifting after many years out of it, and I certainly expect to build back muscle and improving week over week for many years before I can't stem the decline any more, as long as avoid injury or health issues that takes me out of the gym - avoiding time off exercise is the biggest challenge with getting older.
But more than a week and you'll typically need to deload to avoid DOMS. More than a few weeks and it will start taking significant time to work back up, and a lot of injuries happens because people try to rush that recovery and add even more time to that.
If you regularly lose weeks at higher age, it quickly becomes tricky to avoid tipping over into lasting decline.
Lowered the load, increased repetitions and basically nothing for a decade. I can still go almost to the failure, I don't even want to reach it since I don't care about that extra bit. Squats or deadlifts are hard even when not at limits, one feels used body parts for a day or two.
I still add cardio on top of that, its just basic logic of moving around a lot is very good for the body, even if effects are not immediately obvious.
That’s just regular ‘ol DOMS and not a problem.
Tendons tend to respond well to both heavy load or high reps, albeit adaptation in either case is very slow.
These days its more about 15 reps, still 3 sets (plus one just 20kg barbel warmup). When I feel like I could do more, i add 3 or 5 reps, and/or do things slower, especially the lowering part. Weight wise its cca 60kg deadlifts, 50kg squats. I feel like I could do more, but with worse form and thats not a good idea.
There are similar numbers for bench presses, dumbbell curls and few other exercises I sometimes add to mix.
I was never bodybuilder and never looked accordingly but I didn't care, any strong-enough body is attractive to females, good confidence is present and connection to one's body is very good. It was always just training for actual stuff - long hikes, climbing, ski touring etc. Now with kids and after quite brutal paragliding accident that left me wheelchair-bound for few weeks, walked after 6 months and have some permanent changes in calcaneus, I am happy with anything and above is good enough for me, just need to sustain it.