[It's just an echo of her words, but his tone adds plenty of new material - disbelief, mostly, a virtual ton of it. Well, he knows he's young and brilliant is definitely a word you could use to describe him, but... good looking? Aside from Morgan's teasing, he's rarely considered it a trait to count on.
Needless to say there's a fair bit of awkward gratitude in there as well, a little bit of color tinting his cheeks. Inara is a stunning woman, and he's not exactly used to stunning women. Even less so one who compliments him so easily and he's having some trouble working out how to deal with this.]
That's... [Clears his throat.] That's a possibility I haven't really entertained before.