What exactly do you mean by 'gender bent'? Do you mean stories with a narrative constructed around unusual contemporary ideas of gender, or stories retold in order to play with the gender of the original?

If the former, then this is present as far back as Antiquity. There are several myths in Ovid's Metamorphoses in which characters change gender (eg Iphis, Tiresias and Caenis). These transformations are always binary, and always happen for a reason - Iphis asks to become male so that she can marry Ianthe; Tiresias is cursed to become a woman when he kills a pair of coupling snakes; Caenis asks to become a male so that she can't be raped again. Gender identity is never an issue either; the characters are always just as happy identifying as both genders.

If you mean the latter, then a tenuous example could be Hatshepsut, the female Pharaoh of Egypt. Sure, it's not technically a story, but the whole mythology of what a Pharaoh was and should be was a very tightly constructed narrative, based around rituals, appearance and divine genealogy. Hatshepsut manipulated these narrative traditions in order to masculinise her image, despite being established as a female, and become accepted as Pharaoh, which for all purposes worked until her death, at which point many people tried to erase her from history.

I think the problem with finding old examples of 'gender bending' is that gender itself is a relatively recent concept, and the idea of subverting traditional gender roles in this very particular way has only become relevant in comparatively modern history. That's not to say that there aren't more examples, but the examples that there are might not serve the same function.