Why are my parents being such s and pressing charges against my friend?

It doesn't matter that you enjoyed yourself, the fact is it is against the law for a 16 yar old to have with a 20 year old. You are considered a minor and she is not. She is an adult. Your parents are doing the right thing. There is no way she should have been having with you. That stupid girl should have know that you are "jail bait."