"Are you a grownup? Why don't you have any kids?"
I am the same age (25 by the way) as most of the mothers of my students. They all seem to really struggle with the idea of a woman their mother's age who is not a mother herself. In their eyes I am something less than a full adult because I don't have children of my own. Funny thing is, I don't feel like a full adult yet so they must be on to something.