https://wowpedia.fandom.com/wiki/Teldrassil:_The_Refusal_of_the_Aspects
Mesmerized by their discovery, the dark trolls settled along the Well of Eternity’s shores. Over generations, the energies radiating from the lake suffused the trolls’ flesh and bones, elevating their forms to match their graceful spirits. They transformed into highly intelligent and virtually immortal beings.
Chronicle 1, page 93. The night elves were virtually immortal because of how long lived they were, but didn’t achieve true immortality until Nordrassil was blessed.
They did. Which was due to exposure to a titanic amount of arcane energies; well beyond of what the average mage might ever encounter, which was my point. Your average human mage is nowhere near the level of Aegwynn.
Khadgar wondered if Medivh’s mother was here when the land rose, or sank, or was struck by a piece of the sky. Eight hundred years was long even by the standards of a wizard. After two hundred years, most of the old object lessons taught, most human mages were deathly thin and frail.
Aegwynn’s 800 years was well beyond even regular mage, who, while long lived, kept ageing. Aegwynn was a powerful mage before she became the Guardian, which achieved through a process where the chosen mage is furthered empowered by some of the most powerful mages in Azeroth. It’s not a passive extension of your life.
The same book also includes this passage.
And Medivh was there, for to Khadgar it could be no other. He was a man of middling years, his hair long and bound in a ponytail in the back. In his youth his hair had likely been ebon black, but now it was already turning gray at the temples and along the beard. Khadgar knew that this happened to many mages, from the stress of the magical energies they wielded.
Which has been my point so far. Magic can extend your life, but it isn’t through mere exposure to arcane energies, but it can also have the adverse effect on you as well. And in the case of the elves, where it was done through passive exposure, it required a truly titanic amount of magic to achieve it and likely generations of continued exposure to it.