The smirk is more often then not an involuntarily smile that's comes from the way a man thinks.Another smirker. I don't get the appeal.
In that particular instance, when I'm being asked my age, I just threw back at her a challenge and at the same time was amused by her reaction.
Not a single girl or women actually believed me when I lied, even when I said I was a poor ass street sweeper but they all either blushed, felt embarrassed or ran with the joke, thoroughly enjoying my retort.
And yeah, Atom did spell it out correctly too in that it was a form of qualifying by me.