I don't know if the shoulders are a good indication. Some women have broad shoulders( like me) and some men have narrow shoulders.
No but she (if it is a she) might have cut it because of illness or to sell, or because she (if it is a she) was trying to pass as a boy, especially as she (if it is a she) in some sort of uniform. Does anyone know if it is a particular uniform?
many young man of 15-18 retain very fine features, especially if they are not required to be outdoors or doing manual labour.