Any magus does. Just imagine: You spend decades in your lab to master magic, and when you finally emerge, you are old, ugly and you there is this embarrassing puddle forming where you stand â€“ courtesy of your last Twilight episode. So I find it surprising that the Order in general, or House Bonisagus in particular, hasn't yet attempted to invent a remedy. A "Ritual of the Youthful Archmaga" that reshapes the body to its state at the age of 20 and a "Remove the Warping's Weirdness " Ritual that heals the accumulated Warping points should basically make a Mage immortal to (super)natural causes.
But this needs two Hermetic Breakthroughs, you might object. Still, I wonder.
A freshly graduated research Bonisagus starts out with a Magic Theory of at least 4+2 (Level 2 from fosterage plus 40 xp from exposure to at least 20 seasons worth of Lab work).
She can be expected to have a Technique+Vim of 12 or better (two seasons of reading a good summa can easily provide for this), an intelligence of 2 or better and a further bonus from the Aura, which I neglect so I can't be accused of unrealistic numbers.
That results in a Lab total of at least 20: So even a starting magus should be able to research a level 10 spell in one season and gain a +2 risk modificator for original research.
So let's look at the dice statistics:
There is a 3% chance of a botch (1 stress dice + 2 stress die because of extra risk)
How probable is a Discovery? There is a 20% chance of an 8 or a 9, plus a 3% chance of a 1 followed by a 4, 5 or 6, plus a 0,2% chance of a 1 followed by a 1e followed by a 2 or 3. So there is a total chance of 23,2% of making a discovery for a beginning Bonisagus.
How probable is a stabilization of that discovery?
You must avoid a harmful effect (Disaster, No benefit, Complete failure): 77% of the effects fall under this category (this is an estimate, because it ignores the risk modifier: Since only the direction of the modification is already fixed, but the amount is not, I assume that the exact number is even slightly better than 77%).
So the total chance of a stabilized discovery amounts to about 17,7% (0,77*0,23=0,1771), which means you can expect to spend 6 seasons for one discovery.
You need a total of about 30 discoveries (2nd magnitude) for a Hermetic Breakthrough, which is 180 seasons or 90 years of work (if you work 2 seasons per year discovering), including 5 or 6 botches.
180 seasons sounds like a lot, but a dedicated covenant of 4 magi could solve both the aging problem and the Warping problem in about 45 years, which seems to be a small price compared to Immunity to Twilight and Eternal Youth.
Not a single pawn of Vis is needed! And there are beneficial side effects like hundreds of useful spells.
Since the magi only do low risk projects, they get about 3 Twilight points per Hermetic Breakthrough (divided among all the magi working on the Hermetic Breakthrough).
If all 52 Magi Bonisagi worked on this (which the Prima could order), it would take the ridiculous amount of only 7 seasons to find immortality, plus one season to transcribe the results and 30 seasons for the Prima and one other Magus to read the collected works for each Breakthrough: So in only 38 seasons, less than ten years, immortality could be a reality for the Order!
So why hasn't Prima Murion started yet?
Explanation 1: She doesn't realize how easy it would be since she doesn't know the number of discovery points needed.
Explanation 2: She doesn't have enough control over her House to set such a long-term target and doesn't want a small group to do this research because they might become too powerful.
Explanation 3: She thinks it's hubris. Rather unlikely, but stillâ€¦?
Explanation 4: She is afraid of the consequences of immortality, like the power struggles that this knowledge could cause or a Malthusian nightmare of too many mages sharing too few vis-sources.
Explanation 5: Deus lo vult! God makes humans incapable of attempting this project.
Explanation 6: This has happened hundreds of years ago. A small clique of Magi achieved immortality centuries ago and has secretly ensured no one else does.
Explanation 7: Other Magi (e.g. Trianorma's magi) stop her.
Would it unbalance the game?
Yes it would, but it would create story material to last for centuries (think Highlander).