Stef, on behalf of Alex:
I have a whole formula for determining capacity growth in detail, which I won’t share here. But I’ll give you some broad numbers from one of my many spreadsheets.
An Apprentice can’t graduate with less than 250 thaums.
A Journeyman, 450-500.
A Specialized Journeyman, 700,
A Master, 900-1000.
And you’ll probably never see a Grandmaster with less than 3000 thaums.
However, keep in mind that capacity continues to grow with proper stress and novelty. While a lot of people end up stagnating once they leave the University and have settled into their jobs, many continue to grow.
If you were to come across an old man who only had an Apprentice license, it’s a toss-up whether you should be extremely wary of someone who might have had decades upon decades to perfect their Will, (and simply not gotten certified at a higher level for some reason) or if that old man has done the same magic every day for his whole adult life and barely passed 2000 thaums.
Or, if he even casts magic every day at all. If he’s wealthy enough or lazy enough, he might just rely on artifacts and potions created by other people to handle everything that magic handles.