I think all armour must be for man AND women. NO armour for girls or boys only in that game I think! At least, nothing of the sort exist in the original game.
Good news is you can set either the armor to show the same sprite for both men and women, or set two different sprites for men and women, using the SAME armour object in an inventory. How to do that?
Using FT Improver, in Improver_data folder, in ArmourTypes.txt
DIFFERENT SPRITES :
Add the line : {TheNameOfMyArmour;TheTypeOfMyArmor;1;0;0}
In core/sprites/characters, you'll have to have two sprites, one named TheNameOfMyArmourMale.spr and TheNameOfMyArmourFemale.spr.
SAME SPRITE :
Add the line : {TheNameOfMyArmour;Leath;0;sprites/characters/TheNameOfMyArmour.spr;0}
In core/sprites/characters, you need only one file named TheNameOfMyArmour.spr.