I read a short story once that had the following features:
- Bald wizard who was old, but youthful in appearance by magic
- Someone casts spells that propagate in circles and disable magic within the reach of the spell
- At one point, the wizard hits a magic dead zone and ages
- The wizard tries to help a younger wizard who can change shapes
The rest of the details are really hazy in my mind, but it seems like it was in a book with other short stories, including one by Gordon R. Dickson.
Hopefully someone can help me locate this story.