little girl because 少 means
little/small and 女 means
lady/female. It makes sense here. However it does not make sense when I read 少年 because 年 means
year. Is there any reason why 年 was used instead of 男 which means
Shōnen (少年?), shonen, or shounen, is a kango word that literally means few years and generally refers to a typical boy from elementary school through high school age. It is used in everyday conversation when referring to the period of youth, including in legal wording referencing youth, without regard to gender.
So if my understanding is correct 少年 means young person regardless of gender (because
small years or
few years [of living] means the person is still young).
However, this does not answer my question as to why the counterpart of 少女 is 少年 and not 少男.
Some expert opinion on this would be appreciated because the Wikipedia article I quoted has the superscript