Board Thread:Lore Discussion/@comment-30529651-20161117203555/@comment-30529651-20161118000954

Dragonborn can die of age, the best example of this is Tiber Septim.

Miraak being able to live for thousands of years is probably related to H'ermaeus Mora. The situation with Hermaes Mora and Miraak is the most likely scenario for the Last Dragonborn as well. Tiber Septim is a different matter, we can't know anything for sure about the topic and that lack of concrete knowledge/schism is a current plot point. I intentionally left him out though cause he doesn't fill the criteria. From what I can tell the only two dragonborn that have actually consumed dragon souls are Miraak and the Last Dragonborn and that's what I think would grant longer lives. The point of Miraak's servitude to Hermaes Mora letting him live that long is completely valid though. I had considered it before and that may very well be the reality.

I should have been more specific in saying I think there could be a direct relation between how many dragon souls they have within them and the length of their lives.