Other than http://blog.xkcd.com/2010/05/03/color-survey-results/ and specific gender/sex studies, I haven't seen studies that make a distinction between gender and sex. Of course, if you want to make the distinction about biological sex, then you have to define which of the biological criteria and categories you're using, and even then you need more than two categories (http://linuxmafia.com/faq/Essays/marriage.html).
When someone asks if you are male or female, 99% will interpret it as "do you have a penis or a vagina?", not "do you identify as a man or a woman?", nor any other
You seem to suggest that my interpretation is arbitrary, while I think it is the most colloquial. Do you honestly think that a 15 year old girl/boy would see this thread and think "well I am neither of those"? Or are you just deconstructing a very straightforward question by its edge cases to prove some kind of point that I'm missing?
I think my point is more along the lines of "no matter how you ask it, someone is bound to be unhappy, feel discriminated against, etc". I know at age 17 I was not comfortable saying "I am a woman." That meant something to me that I felt I had not yet attained. I suspect minors mostly feel left out as is, just like transexuals feel left out in a thousand subtle ways by all kinds of linguistic implications that there is only male or female.