The current Matriarch of the Amethyst order has been alive for centuries, long before the founding of the colleges. Some of Teclis' original sudents are still around as LM and they are more than two centuries old.
None of the 2 wikis, or 1d4chan, or any of the excerpt quotes of the actual texts about her... ... ever say anything about centuries. (And the 1d4chan entry said that Elspeth has had like all of one appearance in any lore, and has only got a single paragraph about her. It's in the Tamurkhan book thing. SO. Her popularity and widespreadness... is due to fan popularity.)
Her lore: "
For generations the name of Elspeth von Draken, Magisterix of the Amethyst College and arch-wizard of the Lore of Death, has been spoken of in hushed tones in the reeking tavern gutters and vaulted noble halls of Nuln alike. Yet despite these stories few have ever paused to think what exactly the admitted presence of von Draken in the city actually means, and fewer yet could guess at her true power or influence. Furthermore the few foolhardy or overenthusiastic witch hunters, unaware of her relationship to the governing powers of Nuln or too fanatically sure of their own righteousness to care, who have attempted to delve deeper into her business or storm her tower have been swallowed up so completely that they have never been able to share anything they have learned. "
(Death's Timekeeper) "
This hourglass is an ancient and storied artefact, it is said to contain as its measuring sand the dusty remnants of a dead god of old, and Van Draken has spent much of her unnaturally long life studying its mysteries. With it she has perfected some limited measure of control over time and death itself. "
"For generations" means for-multiple-20-or-25-year-periods.
The closest thing you can get to immortal, is looking at the fluff text for the hourglass, and taking absolutely everything in it at its word (rather than rumor) and stretching it to assume that it definitely means she's immortal and centuries old.
And I actually had a bit about Melkoth written up some; talking about how "Yeah, this guy is old enough that he walks with a cane. He's visibly an old guy." "Plus, we're not 100% sure he's actually Melkoth; it could be he just got good enough at casting Melkoth's Miasma, that he then took the name." "Or any other appropriate Grey Wizard bullshit."
Plus plus, I was actually going to mention Teclis's students too... as a negative example. Because, how many of the Matriarchs and Patriarchs that were during Magnus's time, are still around now? Where is Volans? Probably dead, maybe.
And also -- even aside from all that... "1-3 centuries old" is not something that's in "longer lifespan than Dwarfs" range, really. Also also, even that much is for wizards that are powerful and notable and/or have a special circumstance for being able to get more time to live in.
Given how when I just now went to look for Elspeth's wiki entries I came across "several generations" rather than this "multiple centuries" thing, I'm even more convinced that this thing with wizard lifespan is just exaggeration or assumption on people's parts. It's an easy thing to make assumptions and exaggerations about. Easy to make a mistake about, and just assume.