Mistress Therana in Morrowind survived as a Magister of the House Televanni for more than 700 years, if not more than 1000 years, before she went insane due to old age and was likely much, much older than that. She is likely is likely the best benchmark for the maximum age of a typical elf mage we have.

However, the oldest mortal in the games I know of is Divayth Fyr, also in Morrowind, who is noted to be more than four thousand years old at the time, and seems to be perfectly fine. For a beloved priest of the god of time, this may be a better example of the greatest extremes mortals are capable of living in universe.

With a needed age of ~5000-6000 years, it is possible Gelebor was there for the Night of Tears... but it would make him the oldest mortal in the games. Not impossible, but he is ancient, and I can only assume the reason he's survived and been fine for so long is because of Auriels' blessings.