The future

My boyfriend and I have been together for 5 months now. Although I know it’s too early to be thinking about a baby right now, In the future I do want one. My boyfriend already has a 7 year old daughter and a 4 year old daughter. He’s 28 and I’m 20. He has mentioned several times around his mother that he doesn’t want anymore kids, and he has mentioned to me several times he wouldn’t mind having one more. As a 20 year old step mom, I do treat and think of his daughters as my own and they even call me mom (don’t get offended by this, their real mother is not in their life). Should I talk to him about it or should I wait it out? I definitely want a baby in the future.