Actually, how long do wizards live? Human wizards, I mean. Because Dwarfs lives for centuries. Possibly millennia. Whereas the usual human wizard, even a powerful one, is probably lucky to live past a century.
Or are we functioning on, as chocolote12 put it, "Well, you see, it was mentioned once as a potential option, so we practically have it already" logic where "Well you see, it was mentioned that Gold Wizards turn themselves into Gold once, so therefore this means Golds have immortality for sure (rather than a rumor or assumption about it) and therefore all wizards are expected to be immortal" "Lots of posters have talked about this Gold Wizard thing, over many years and many threads of warhammer fantasy, so it's practically accepted knowledge now."
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How many ageless human wizards do we actually know?
Because I don't think that we know enough immortal-for-sure human wizards to say "Wizards are ageless by default." Maybe you have some wizards achieve agelessness or a form of immortality. But it is not something to be assumed.
Also? I would super not bet on Mathilde, specifically, living past a century. Because the way we currently act, we'll get ourselves killed within that century. Unless we retire from dangerous stuff, and be mainly a researcher, scholar, and Loremaster of K8P. So even if wizards were ageless somehow, I would still not bet on Mathilde specifically outliving a Dwarf.