[quote=Rin]
Going by her appearance (mostly the fact that she's not a wizzened old crone), I'd assume the latter. XD ...Although this is partially because having our Old Man Genocide analogue go missing at some point in the past seems like an interesting plot hook to me but um yeah.
[/quote]

Unohana was around when the Gotei 13 were formed, and she didn't age a day, though. So age isn't a factor. Kyoraku and 13th Division Guy might have also been alive then, though unlikely to have been captains (though they were trained specifically by the old geezer). XD