[that isn't a new one either, so his answer is almost reflexive:]

I was around your age [guessing, anyway, by the look of her] during the Battle of Yavin. The Empire didn't care how old any of us were.

[he's really looking at her now, though. something about her doesn't quite match the normal surprised response or token protests. in fact, just his lightsaber is usually evidence enough to most people, since no one else alive in the galaxy carries one around, let alone with the signature green blade. he's already seen a lot of strange things today...

so he asks:] Why can't I be Luke Skywalker? What were you expecting?