I taught at every gym in a large city and my advice to anyone wanting to send someone over 50 into one of them is to perhaps start there but move on. I taught a true high intensity interval training program until I was 56 and every gym begged me to tone it far down. I finally was fired from a high end gym because they had developed an ultra low intensity version of the class I taught and I refused to teach it.

What someone over 50 will get shunted into is a Tai Chi style class where you'll lift your arms up and take three steps, and hey, see you next week. I know that everyone has to start somewhere, but if you don't advance out of that class and ultimately out of the gym, you aren't going to make much difference in your life.

The typical chain gyms know most people don't actually want to do anything but say they went to the gym. They absolutely cater to that market. If you want to start there, fine, but move on.