Obviously Magneto ages more slowly due to his connection to the magnetic poles. It's the same principle that has people wearing those magnetic bracelets (like Tony in Avengers actually). It's a subconscious process, but he's able to delay cell decay by taking pressure off of his body. Xavier on the other hand, was actually much older than he seemed but he projected a younger image due to his rather well-established ego until the brood forced him to get a new body. Am I eligible for a No-Prize?