I grew up working on and then also operating a NW IL grain and livestock farm. It was very physical. The three square meals a day were a necessity. Then I became a truck driver. I realized real quick that I needed to eat less and do some exercising. The sit all day jobs should only require half the calories, unless there is a dedicated exercise regimen.
At age 67, I am not the slightest bit interested in having big muscles, nor going to a gym. I do some good old calesthenics and core exercises on the living room floor, go out to the garage and get on the old Nordic track ski machine for a few minutes, then go run up a 200 yard stretch of the dead end road, in front of our house a few times. It all takes about 35-40 minutes. I do this about 3 times a week. Sometimes mixing in a few miles on the bicycle.
Rebuilt nordic tracks are cheap and give a good workout. I bought mine about 8 yrs ago on ebay, and haven’t needed any parts for it, but they are available. Just make sure that there is tension on the flywheel spring before stepping into the skis. Other than that they are easy to get used to.
I do not use any machines in gym to build muscles. It is strictly cardio-vascular exercise machines that I use. such as treadmills, ellipticals, exercise bikes etc.
At age 81 all I need is to keep heart strong and lungs strong.