20 yr old bf

Okay so my boyfriend is 20 and I am 17, he wants to start a family with me and I’m still in school. I’ve noticed that he tries to have sex with me without a condom on hoping I don’t notice. He’s talked about how he wouldn’t mind if I was pregnant and that he wants to have kids with me in the future but I’m not ready yet. Any tips on how to talk to him about this?