They just can't comprehend it

Most people get my decision to be childfree.<br><br>My dad doesn't. He is a lovely man, but he's a family man, and absolutely loves his children. He's a great father.<br><br>Every now and then he will say this: "How can you know you don't want kids? I always knew I wanted kids. If you don't try, you can't know?"<br><br>This makes me angry. I don't want to have to reason with my father about why I don't want kids, but I don't want to ruin our relationship either.<br><br>I have no idea how to respond to this.<br><br>Edit: I am a 22 year old woman.