No, dxb, I think you missed the nice distinction between a [young] lady and a [young] person. Or a gentleman and a person. You must be too young to know about this. It's not a matter of age, discretion or predictability. It's a matter of class (pronounced clahss, in the Pom manner).
In the olden days (up to the 1930s maybe) the term "lady" or "gentleman" had quite a precise meaning, and it had to do with social class. The upper classes were not about to recognize a pleb as an equal, and those who served the upper classes had to be particularly careful not to appear to be recognizing a female person as a lady when she was not. Hence, if the butler needed to inform Madam that someone like Eliza Doolittle desired to speak with her, he might say something like, "Madam, there is a young person who wishes to speak with you." He certainly would not say a young 'lady'. That was what WoDoc was getting across in his Mikado example. These conventions are now as dead as the dodo almost everywhere, although I suppose there may be a few Col. Blimps and their female counterparts still holding the upper class fort in nursing homes in remote parts of Britain.
