Centuries? Can Kossiths even live that long? I can imagine a blood mage getting ageless imortality, nit nothing else about the other classes would suggest extended longevity. Plus Arcane Warrior is an Elven magic. I'm surprise the kossith, who are typically magic-phobic even outside the Qun, would know about such arts. Though I'm suspecting artistic licence for how or when kossith set up any sort of village in Fereldan(Given thats where Flemmeth lived most if her life).