My excellent fitness trainer told me that it takes 2 years to pass from the beginner phase of weights, regardless of age. That has nothing to do with amount of weight moved; it's just about getting the forms down right, ramping up past the beginner's need for any machine training, and getting to the point of effectively pushing the envelope of your innate abilities - whatever they are - past the initial "waking up" phase.
The antique fitness recommendations of simply running, jogging, walking, rowing, swimming, spinning, etc. have long gone the way of the low-fat diet. Well, the low-fat diet was totally wrong, but low-resistance cardio (only if intervals) does still have a place in the Fitness Triad of Resistance, Cardio, and Calisthenics.
Weight Lifting Important for Health
As an ectomorph with a runner's build, I will never bench at the levels of the shorter, muscled guys with short arms. No problem with that. I just want to maintain and improve fitness and not be, or look like, a weak, lazy schlub. That's why I did 45 pull-ups this morning (ok, jumpers), and 5 sets of deadlifts with increasing weight each time. It feels quite good when you stop.
Barbell squats kill me, or will. Matchstick legs and no ass, he says. I ask him to please wait until I finish my coffee to insult my God-given physique: I am easily offended and may need to retire to my Safe Space at the local pub.
Mrs. BD is a more sturdily-built mesomorph. She enjoys the weights part of her program more than I do, but she can't do barbell squats (iffy knees). She does deadlifts, snatches (which I can not do due to one bum shoulder), pull-ups, dumbell rows, bench press, curls, press-downs, pull-downs, overhead presses, and plain squats. Interestingly, doing weights has done a lot of good for her knee issues, just as the trainer predicted.
Rule of Thumb: Make everything a bit harder each week and aim for the goal of condensing everything in the efficient multi-muscle group basic exercises. Takes a while to get there, maybe a year. If middle-aged or +, one 3-6 set of each resistance exercises/week is enough.
Photo above: Your editor last week, after one year of resistance training. Think I should cut my steroid dose a bit yet? Truth is that no middle-aged guy with 5-6 hrs to spend on fitness including only 2 hrs of weights in that will bulk up very much. Mainly weight-redistribution will occur. That, plus energy and vitality. Any gut disappears even if you like beer.
Photo below: Mrs. BD after one year of the Fitness Triad plus Atkins diet. Keep it up!