Talking to him about having a baby

So. Here's a little background. Please don't hate, if you don't have anything nice to say, please move on to another post.

My partner is 43. I am 22. He has 2 children, 11 and 15. Our relationship is steady, and pretty serious.

We've had random conversations about what we want for the future, but never in a legitimate planning sort of way.

He's seemed/been very open to the idea of more kids. He's in great shape and very active. We talk about how he's pictured me being a mom/being in labor, and so forth.

Sometimes I feel like he's not so sure though, which I totally understand. However this is something very important to me and something I want to start planning for. Even if it's not for another year or 2.

How do i talk to him about it without seeming desperate or without making him feel obligated to want exactly what I want.

I'm kinda lost ladies 😕