How old do you have to be to go to cage fighting?

Me and my friend want to go watch another friend get beat up.. mean a little bit but he would do the same to us.. so its okay.. and we were wondering how old you have to be? And are there different types of cage fighting if so what one would beginners be in? or just name all them..
I don't want to cage fight.. I am more of a prepy girl that likes sports like drill team, cheerleading, and volleyball.. I have no intention of ever being a cage fighter...being in fights scare me but i like to watch them..