That's quite a spread, even the oldest magus in the Magi of Hermes book is I believe only 105 years past gauntlet (or does Gwidion top out at 120 years). The thought of the numbers for a magus 150 years past gauntlet is a bit intimidating. The way I see it magi 45 years past gauntlet have had time to see to a few of their biggest their weaknesses and develop a fair suite of tools to do what their interested in (look at the final versions of Hugh, Lambert and Tolidies for examples). Magi 150 years past gauntlet have probably more than twice as many xp and 4x's as many spells and items.
This list jumped out at me because I've been working on a version of Ranulf (from Magi of Hermes) at 75 years past gauntlet. (I'm not playing in an Ars game at the moment so I have no personal character to mull over possibilities with, yet I still think game mechanics every now and again).
I decided that the three things that he'd work on in the time period were, doing things with AC connected fires, getting a familiar, and being a better combatant.
Now the deal with Ranulf is that as an apprentice he studied up on pillum of fire, he's got for levels of mastery and some spells to make it a pillum of freezing fire. However in the 60 years since apprenticeship he's never applied himself to developing combat spells or items particularly seriously (there was the target group wizard's boost and some defensive stuff but by and large his spells were designed to avoid combat by placing lots of fire between potential combatants not to actually hurt anyone). But with three or four years in the lab at 65 years past gauntlet I've made him preposterously scary. The main story is that I've made him preposterously scary at something that he wasn't particularity good at before and it only took four years. As characters get older, the time it takes them to go from "not something I'm especially good with" to "I'm so darn good at that even the those who've been studying the subject for decades might not be able to perform better than me" becomes shorter and shorter.
At 60 years past gauntlet (where ranulf was) a magus is right in the middle of that age distribution (55 are younger than 60 and 52 are 60 or older)
If a 120 year past gauntlet magus decides to become an expert at something I'm thinking that 3 years in the lab would net him about 8 applicable and formidable spells or devices (levels 20 -50). I can't think of an endeavor which needs more than that.
So a change that I need to make in my perception of the setting (if I want the setting to match the rules) is how quickly an "adult" magi character can become good at something. Just because four years ago old Gwidion wasn't good with dealing with mundanes and Maris couldn't find a silver deposit and mine it out completely within a week doesn't mean that they can't now (if they had the proper motivation).
Guardians of the Forest has three magi who are approximately 160 (real age), which probably makes them somewhere between 130 and 140 by hermetic age, Caecilius ex Bonisagus at Durenmar, Shadritt ex Miscellanea at Dankmar. and Eule ex Bjornaer at Fengheld.
Yes, if an "adult" magus really wants to they can become really good at something quite quickly. It still takes seasons though.
Which means, that motivation is, I think, the key here.
Generally, "adult" magi have "adult" things to do. They are busy in their lab working on some vast project, or they are busy shepherding apprentices around, or zoned out on some Mystery Trip, or doing something else. They are not just sitting around waiting for something to do.
So, yes, if some situation crops up an "adult" magus can go away into his lab/library for a number or seasons, and return with The Answer. However, even assuming that the problem is amenable to waiting for a number of seasons before being solved, there will usually be other quicker options. Which largely boil down to:
a) paying a real specialist to sort the problem out now, or
b) attempting to hack-up a solution to the problem in an "innovative" way with the spells, Arts, and other tools that the magus has to hand right now.
I know my magi (~100~ years past Gauntlet) certainly has his projects. The SG laughs when I mention the fact that I have way too much to do. The short list is:
Finish my NoP initiation, and go defeat that Spirit.
1a) Put that stuff into my Talisman (I haven't forgotten Erik)
Make my improved Armor: I haven't done a real upgrade to my armor situation in sixty years or so.
Make that shield I have always wanted.
Throw a couple of things into The Bond. She's been bitch'n about that for a few years now.
I have about twenty spells on my "Wish" list.
The Flambeau (Amicus) needs a nice sword. I need to put a few seasons into "Covenant Work" anyway, so that should do nicely.
Train the new Grogs. They need their Captain to take them out and shake off some dust. (Vikings always need to kill someone after all)
8 ) I need a few tools for the lab. I figure about three years and I can have that done.
I have about twenty items that need identifying.... Yeah I'll get around to that soon...Maybe next year...I really want to find out how that tower sculpture works. I've had that dang thing for about forty years now...
I still have that dragon egg... What am I going to do with it.
What am I going to do with this Basilisk, now that I bound its power?
Anyway, that's a start...
Erik statement is certainly on target. The older my Magus gets, the more projects I find backlogging him up. Though I get to 'knock off' that odd book now and then, I still can't get to the bottom of the list...
Ezzelino's list is good by the rules.
I would set the oldest magus's hermetic age a bit higher like 200-250 years. He/she would be a fairy blooded magus who didn't deal much magic in his/her life thus avoided twilight.
The second oldest would be somewhere about 190 years of hermetic age.
The third around 170.
And 2 magi at 150-160.
you could even go to 300 years (that is around 275 past gauntlet) if you got your (good) longevity ritual at 40 years old and never got warping points by other ways...
so you go have as Birbin again says 200-250
and 250+ (probably only one in a tribunal or none...)
I wouldn't necessarily make your oldest magus/maga fairy blooded. There are lots of ways to become ageless in the game: saoshyant's elixir, immortality of the forrest, guardian of nature, and path of the body come to mind. There is the lesser elixir in the alchemical mysteries. Finally there is the possibility of one of the magi within the past hundred years having a magical focus in ageing along with a few other applicable virtues and studying the heck out of the correct arts and theory, getting a focused lab set up, arraigning to get help in the lab and thereby creating ageing ritual lab totals of >120. Let's not forget the effects of a good medical regime (from A&A), a strong bronze cord, or extraordinarily healthy food from City and Guild. (and of course there is the possibility of the true immortality mysteries as well).
So because there are so many different ways to extend your life I think that no one of them should necessarily be associated with the oldest magi. What should be associated with the oldest magi are things like careful sorcerer, a strong golden cord, and flawless magic to avoid double botching and sending yourself into permanent twilight, and temperament that makes avoiding danger a way of life.
I remember one character who experimented and got 80 on the experimentation roll (1 1 1 10) (we always use stress dice for experimentation) and had a very good lab tot (he was a third or fourth generation character who was a talented bonisagus with one of the best mater ever.
My ex-misceleana, specialist of creo corpus (she is pharmacopeians) got -15 on her aging rolls, without experimenting.