Decrepitude and warping eventually get every magus. In the section about longevity rituals there is a statement regarding the upper bound:
Magi of two hundred years or older are rare, but not unheard of.
How long should a magus be expected to live? What is the median age of death for magi?
Magi should plan to live to 100, suspect they might get to 125, and could specialize and live to 200; although not without significant favor from the SG. Plus or minus how the saga is played; as many saga will end before 50+ years pass. There is no RAW answer for this in the 5e rules. Very senior magi in the descriptions seem to be 120+ years old. Player magi might be lucky to live past 50.
Sub Rosa (a fan mag for Ars Magica) issue #14 has an article called "Demography of the Order of Hermes" by Mark Shirley which may be useful in answering this question statistically.
