I understand that you are taking about muscle gains in mass versus strength, but at age 72 now, I am stronger than I was at 35 or 40. After 4 years on 5-3-1, I have reached 340 on my deadlifts, 300 on squats and 250 on bench press and I expect to continue to add to those totals (Not impressive numbers for you bigger, younger and stronger guys, I understand that). At 5’10”, 180 lbs, I’m not and never have been a big strong guy. My point to all my rambling is, as relates to muscle strength versus size gain, my experience has been that slow and steady progression works well into your “senior years”. A solution may be a change in training regime, with more emphasis on rest/recovery and increase in protein intake while keeping calories at or near your current levels. Old age has been good to me despite some setbacks (cancer, knee replacements, back surgeries). It can be good for all you guys too. Keep a positive attitude, focus on what’s really important (overall health and relationships) and adjust training and nutrition to find what give you the results you seek. Good luck.