[He doesn't say anything about the first part. Mortals don't understand magic - so Betty is skeptical. It's not exactly flattering, when it's not like she can do any spellcasting of her own. But still.
He turns to the second part.]
Why, would you leave if I told you I was an old man?
no subject
He turns to the second part.]
Why, would you leave if I told you I was an old man?
[His smile is charming, and pleased.]
I'm eighteen.