From the old-school Southern male perspective, I was taught, and still believe that all adult females are to be considered "ladies" until their behavior clearly demonstrates otherwise. And even then, you give them the benefit of doubt.

Foreign languages have their own nuances, too... I remember that in German, the proper reference is Frau (plural Frauen) or Fraulein, occasionally Dame or Damen (plural). (hint, the feminine restroom is labelled Damen, good for a joke or two with the new guys who can't tell the difference betwen "da Men" and "Herren" (which is how the little boys' room is labeled, btw.) but that's a whole 'nother story.) Using the term for female, weib, or weibliche, is considered derogatory in polite circles, and is usually refereing to livestock.

But then again in gender non-specific circles, I confess that I'm one of those who typically refers to everyone as "guys," regardless of age or gender.

Tom