The veteran actor starred in three X-Men films as the magnetic villain and movie bosses are said to be planning a new movie to reveal the character's beginnings.
The project will follow in the footsteps of X-Men Origins: Wolverine which featured Hugh Jackman's X-Men alter-ego.
But McKellan, 70, is adamant a spin-off featuring Magneto will not involve him - he's too old to play such a demanding part.
He tells EmpireOnline, "There's meant to be a Magneto script floating around, but I've not read it, so I suspect it wouldn't involve me. I think it would be about the younger Magneto, and the most I could hope for would be to top and tail that. They can't have someone whose face is as lined as mine any longer!"