A kilt is a skirt no matter who wears it. Nomenclature is not intended to limit, but merely describe accurately for the sake of comprehension. Not all skirts are kilts. To be a form of kilt it should have pleats in back and aprons in front.

A military style kilt, whether worn by men or women, say in a pipe band or as a highland dancer or athlete, may for simplicity be called simply a kilt.
A mini kilt is shorter and intended for, please only, women.
Kilts over the knee are referred to as kilted skirts or kilt skirts.
Kilts to the ground are called hostess skirts and are considered formal.

Dancers and athletes of either sex are required to wear undies. Soldiers are required not to. What you as a civilian do is entirely your own business and not even your boyfriend's if you don't want him to know.