The best answer that I can offer you is that fitness is not a “cookie-cutter” business. Over 40 year old males come in all shapes, sizes, and ability levels. In order to determine the best muscle-building program for a man over 40, we’d have to at least know his health history, his body type/composition, and we’d have to know a little about his current activity level, at a minimum.
It’s not so different from an under 40-year old. The increase in intracellular proteins (actin, myosin, troponin, tropomyosin) appear to be mostly related to the load on the muscle, not the age of the owner. The key seems to be taking the muscles to temporary failure, to activate the type IIb fibers. So, with the exercises that you are doing, perform 8-12 RM (that means max effort at 8-12 reps.) Check your kinesiology to be sure that you are working the muscles in appropriate major muscle balance.