Priest - Female
Wizard or Sorceror - Male
Witch or Sorceress - Female
Barbarian - Male
Amazon - Female
Now, these would be the same in skill set and such, but it could imply lore into the classes. Meaning you could have a frenzied Male Barbarian throwing spears like an Amazon. Likewise, having a strong Female Amazon that you play like a close combat Barbarian.
Mainly about Barbarians, but I see them as stemming from some sort of Barbaric culture (bandits and vikings). Orcs are an excellent example at a "civilized" strand of Barbarians in my opinion. "Stronghold" in Heroes of Might & Magic as well. An established Barbarian society.
I've always viewed the women of these tribal Barbarian settlements as something less masculine, namely something more akin to Amazon. The hunters of the strong and proud male dominated Lion pack.
Unisex, but: Barbarian Fighter or Soldier?
The rest of the classes feel to me pretty unisex. Fighter doesn't really say "Male/Female" about it, but it could be a part of the aforementioned Barbaric culture. Unless "Fighter" gets a different title, such as "Squire" or "Soldier" or whatever else is fitting the role of the Fighter in the world. About Squire: I absolutely love the feature in the original Final Fantasy for the NES, when you meet Bahamut for the very first time and it's "Oh snap". Then you do a long quest for the Rat's Tail, which you then return and you become "Knighted" (Fighter becomes Knight). Can Factions help you grow in status among the people? Or hide from their sight?
Does different Factions provide different types of experience?
What's the difference between the Barbarian and the Fighter and what is it that makes the Fighter a Fighter and the Barbarian a Barbarian?
Wizard and Witch, to me, feel pretty granted as is. A female "Wizard" does, however, sound a bit odd. The skillset wouldn't differ between the two, only their titles. And whenever "Class" is mentioned it accounts gender as well in dialogue? So the result becomes "Witch" instead of "Wizard" if you have a female "Wizard". The same goes for Barbarian/Amazon, they would both have the same tools as the other in terms of character building.
Paladin and Priest, would not be the same skillset (A Paladin is a Paladin, a Priest is a Priest), but only female can be Priest and only male can be Paladin. I'd like to advocate for dialogue options if you create a female Paladin, meaning it wouldn't be "off limits" at character creation, but lore-wise for your own party it could be something interesting. With few male Priests in the world, having one in your party is like having a Paladin "defect" perhaps. Trash, in their "Glorious" eyes, even if you can woop their ass right on the spot. Of course, reputation should play a big part too.