This is not the web site for a health club, it is a question site for members of the International Association of Fitness Professionals
If you go to google maps and look for fitness centers in a radius close to you you can probably find quite a lot of places with senior exercise classes.
You might also ask at your doctor’s office, as they usually have places they can recommend, particularly if there is something that is partly covered through insurance.
You can also try contacting your insurance company.
These are a couple of links you might find helpful. Silver sneakers is a popular class style with instructors trained in the unique needs of seniors.