I've heard married couples say, "The first fifty years are the hardest." Fortunately adjusting to your workout routines doesn't take that long, IF YOU MAKE IT FUN. So many people, literally, go "by the book" using an exercise card to record, weight, reps., & sequences. Besides interrupting a good work out & boring the heck out of you, I see minimal benefit in this.
A year later they are still following the same routine, but have increased the weight and/or reps. No wonder it starts feeling like work. Over many years, I have seen much better results when people vary their routines doing a complete body work out each time, working all muscle groups & on as many planes as possible each day that they work out.
There are two approaches to work outs, body building & body conditioning. As you can see, I am an advocate of body conditioning. I have no argument with those that prefer body building, but over the years that I have studied physical fitness I have noted that, comparatively speaking, bodybuilders seem to have less range of motion and lose their flexibility/mobility as they age. I teach boxing, & I have noticed that, generally, bodybuilders have slower hand speed.
Any workout program is better than no workout program. We are all different & should tailor our program to fit our needs. Those needs will vary, to some degree, all the time. That is why I recommend you not be rigid in your program. Change it employing all the training methods, not just resistance. Don't always work in the same sequence. You will find this beneficial to both mind & body.
Certified Personal Trainer/CIME, ex-boxer, ex-Army Sgt.