This is a major flaw, progeria causes the victim to age at a excelerated rate.
Now my question is this:how would it effect the ars magica world, magi and otherwise?
There is already such a flaw (Age Quickly)
The mere existence of such a flaw would not affect the game world noticeably at all.
Individuals with such a flaw, and those close to them, would of course be affected - just like with similar afflictions in the real world, and the reactions would be the same.
Ok then