I had started back on weight training about 1990, I used weights in high school for football and track. But it became fully "Body Building" to me, as that bug hit me hard! I was 37 then, and by the time 2001 came around, when I was 48, I was at my most muscled of my life!
I had gone extreme at times; 10 sets of 10, but I did it too often, Overtrained! Then I went with higher reps, with 2 or 3 body parts per day, and I had switched them up at times, bi's with tri's, tri's with chest and shoulders, etc.
But by time I turned 48, I only worked out twice per week (maybe it was a 6 day week thing), and I changed it up by warming the body part up, going Heavy (heavy for me) for 6 to 10 reps, and I THINK I only did 3 sets. Then the next time on those same bodyparts, 6 or 7, 8 days later, I went higher reps, 15-20, yet low or medium weights. I was no longer overtrained, I had great energy, as for some of that time I walked about 3 miles a shift at work (Campus Security). I really was at my most muscled at 48, because by then, I wasn't at the Campus job, and I just laughed at people who said you always have to go heavy, you always have to do many sets, etc.,etc.; yet I did it by doing less. I was not on gear, I did take the legal hormones back then, but I felt like they didn't work, but possibly they did.
But then my back started, nothing to do with weight training, the Docs actually said that probably kept me stronger and healthier before my spinal discs became degenerative, and the chronic pain started early in 2002, and has increased every year since then, so of course no more body building, at least what I did; I use Power Bands when my body can handle it.
So in my case, I actually got better in my mid 40's! And with lower sets and reps, and actual weight!