I did Jazzercise about 10 years ago. I love to dance but am certainly not trained; and of course it's not really a dance class but an aerobics class.
There were women in there of all different ages and shapes, from the young, slender, fit 20-somethings to grandmas. In fact, our instructor was a grandma!
I think the basic thing is to be able to (at least somewhat) stick to the beat, and be able to go the right direction when there's a move involving going up and back or side to side. You don't want to be going right when everyone else is headed left!
One of my friends in the class had really bad knees, but just did a very low impact version of the moves, no jumping. She kept up just fine. One of the great things about Jazzercise is that it really is for pretty much anyone. You can make the moves small/simple/less strenuous, or big/fancy/more energetic as you want.
I loved our instructor, who was funny and encouraging, but we did have someone sub once who I couldn't follow. She'd take a basic move and add all kinds of extra elbow pops and hops into it, and I just couldn't figure out what I was supposed to be doing. I think the instructor really makes the class, so if you don't care for one, try another one with a different instructor.
