Keep Registration Forms for Church Bible Camp?

Hello!

I co-direct our church's summer camp ministry (South Olive Bible Camp). We have been operational for almost 50 years. We are certified with the State of Michigan. I have been accumulating a lot of camper registration forms over the years and want to thin out my file cabinet. I am wondering, legally speaking, how far back should we save camper registration forms before shredding them? I also have former staff applications, reference forms, health forms, etc. from many years back as well and was hoping to purge some of them. However, I want to do what is legally responsible. If anyone out there can offer some advice, I would greatly appreciate it. Thank you!