Am I overreacting?

My boyfriend who is 5 years older than me hung up a little calendar in our car of naked porn stars. I told him I feel uncomfortable with him looking at it everyday not only because I feel disrespected but I don't like the idea of him sexualizing other women. When I told him this he got angry and said I need to grow up and that I'd understand when I'm his age (23). I know I can't stop him from ever seeing another pair of tits again but he is choosing to look at naked pornstars over me and my feelings. Am I overreacting? Is there another way to express to him how uncomfortable I feel about it? What should I do ladies?