How can I deal with immature people? What should I do?

I have a friend name Zaria and we pretty much get along with each other,but I dislike her immaturity. I would play with her a little,but I take stuff very serious. She's too immature. I tell her to stop playing when she takes things from me and keep it away from me or hit me,but she keeps doing it. She finds me too mature and I find her too immature,but obliviously we don't like each others action. Even I have some friends who acts just like her. I once told Zaria,Micheala,and Allison that I dislike the childishness. They respond that I need to act childish like them because I'm lame. I didn't really listen. What should I do to get over it?