How do I (F22) put boundaries with my long time crush (M22)?

I’ve had a crush on this guy since school. We’ve always kept in touch via Instagram and other platforms. Recently, he told me that he’d like to explore dating with me, so we’ve decided to get to know each other.

He’s currently in NDA training, so he barely gets time to talk. But when we do, he mostly brings up physical intimacy—not in a very sexual way, but in a flirty way. For example, he says things like, “I can’t wait to kiss you” or “So, when are we practicing for having kids?”

This makes me wonder—does he assume I’ll sleep with him on the very first day? Or is that all he wants from me? I don’t know how to make it clear that I’m not that kind of girl without making it a big deal. Maybe he’s just joking, and it’s too early to ask what page he’s on since we’ve only had three conversations about this.

I want to gently set my boundaries without offending him or making him pull away. At the same time, I don’t want to come across as too uptight or overly serious about this too soon. Any suggestions on how to handle this?