Should I Be Offended?

I'm transcribing an interview for work. The person I'm interviewing asks, "How old are you?"
Me: Um, older than you. (I know this, as I have his bio).
Him: Oh, okay. You sound young. I thought you were like a student.

I feel like I need a sign I can wear that says, "Yes, I am a grown-up." Of course, my actions probably belie that.