I haven't found any info on the lifespan of the Orsimer, which makes me wonder when Urag talks about protecting the library since the second era (I know he can't be that old, but he talks about it as if he was there). IIRC all Mer have lifespans well over 200 years.
I don't remember where I read this (and if the source was legitimate or not), but I recall reading that the Orcs were cursed by a god for betraying someone or something. That's really all I remember

It's possible Urag has used magic to prolong his life, but I doubt he would have been around since the second era.
EDIT: http://www.imperial-library.info/content/varieties-faith-empire
Orkey (Old Knocker): A loan-god of the Nords, who seem to have taken up his worship during Aldmeri rule of Atmora. Nords believe they once lived as long as Elves until Orkey appeared; through heathen trickery, he fooled them into a bargain that 'bound them to the count of winters'. At one time, legends say, Nords only had a lifespan of six years due to Orkey's foul magic. Shor showed up, though, and, through unknown means, removed the curse, throwing most of it onto the nearby Orcs.
Doesn't really explain much, but it at least says that the Orismer now have shorter life spans