@SeasonedRP I understand that the older guy is effectively caught in a fork. One one hand he recovers less effectively. On the other hand he also responds less well to the training stimulus -the number of genes whose expression is altered is much reduced. There are a number of studies on this in mice and men. Here is one such article. Its worth reading a few. www.sciencedirect.com/science/article/abs/pii/S0047637400001780

This means that as you age, you have to use your resources wisely. Some age earlier than others and in the end if you know your body, you should be able to pick up on when things change for you. In the late 40's there is usually the most pronounced change for men and things then carry on gradually declining until around retirement age mid 60's when you take another more pronounced dip.

Young guys only need a small stimulus to get gains and they recover fast. Its why young tradesmen who don't even do any sport or training usually look great on a construction site in summer with their tops off -work alone is enough stimulus, they can go out drinking after and still look great. When older tradesmen do not do any sport or training they look worse than office workers when they take their tops off in summer. The job is actually driving these guys down as they are not fit and can't recover from it. The stress usually makes them fat as well and they often live less long than desk jockeys.

There is no need to change things up until you see you need to. Then it becomes a case of making the stimulus felt enough yet not slamming yourself beyond your recovery ability. An extra set is said to sometimes be the answer but it will have to be lighter or less frequent or else it will push you too far into muscle damage to effectively recover in time for the next session.

I am not really a lifter, so I can't say the exact things lifters should do but the aging problem of poor recovery and poor stimulus response is the problem one needs to work around somehow.

Lifters over 40 are told that their training needs to be significantly different from that of younger lifters. The standard advice is to reduce the volume and frequency and up the intensity. So instead of squatting twice a week doing, say, a 5x5 routine, they might squat every 10 days doing one or two worksets with 90%+ of max.

Whatever the merits of that advice for others, I've been doing the complete opposite and making steady progress. I'm way past 40, but I do a squat or squat variation 3 times per week, bench press or bench press variation 4 times per week, and deadlift or deadlift variation 2 times per week. I use fairly high volume and do most worksets at around 80% of max, with the second most being in the 70-75% range. I've gone to 90% maybe twice in four months. I designed this routine based on a template I posted here a few months ago and on past experience with set/rep schemes that worked for me.

Maybe I'm an outlier, but I'm skeptical older lifters need to change much as long as diet and recovery are on point, and certainly not at the tender age of 40.