Like @SarahGabriella say Gerald is character from the book and game was base on the book, so ofc you can't change his gender or is he tall or small, fat or slim.
Long ago i also comment that V character creation and options about her Hero/Life Event/Why Night City are copy of Mass Effect Shepard background, people start to talk how it is wrong and how Shepard is established in Mass Effect Lore, point is both are defined character.
Blank sheet character is Watcher from PoE 1 or your Duke/Duchess from Pathfinder Kingmaker.
Also OP ask more about if he can dress his male V in female cloths if he want that.
I do realize that Geralt was a book character that was kinda my point but it dosen`t matter now you have given me a game i haven`t heard of before Pathfinder Kingmaker to watch on YouTube