Originally Posted by azarhal
A new protagonist that "work" for Geralt, because he's now too "old" would be the way to go.

No, it wouldn´t.
Playing a sorta I´m-too-old-for-this anti-hero character is one of the intended defining characteristics of the games and getting rid of it for the sake of fresh out of school main protagonist would certainly not make the third game inherently better. If anything, it would make it less unique.