How old should you be to be in zumba fitness?

There are Zumbatonics classes for 4-12yr olds. I took my granddaughter to a couple of my Zumba classes when she visited me this summer. She enjoyed it but found it strenuous. This had more to do with her seditary lifestyle. After all, I am over 60 and do 4 classes a week. I think it is a great way to get children to exercise. Music they can relate to and gives them confidence.