Is there a written tradition that would explain why John the Evangelist is often depicted in art as effeminate?

John the Evangelist is often depicted in art as effeminate (e.g. long hair, clean shaven, gentle face), as illustrated below. This is especially apparent when compared with other males in the same painting (e.g. Da Vinci's). Obviously the artists didn't know what he actually looked like, but is there a written tradition that would explain this common depiction. [Da Vinci — Close-up from *The Last Supper*, circa 1497](https://en.wikipedia.org/wiki/The_Last_Supper_(Leonardo)#/media/File:%C3%9Altima_Cena_-_Da_Vinci_5.jpg) [Piero di Cosimo (Piero di Lorenzo) — *St. John the Evangelist*, circa 1500](https://en.wikipedia.org/wiki/John_the_Evangelist#/media/File:Piero_di_Cosimo_(Piero_di_Lorenzo)_-_St._John_the_Evangelist,_c._1500.jpg)