It takes forever after it looks like they've alredy hit the master level, to get that last tiny bit of experience. It will drive you mad. They do eventually get there, though, if they are young enough.

I had a guy die just before he should have turned elder, because an event when he was young made him lose some experience. He was 75 and had been at the master line for about 2 village years and if he'd just lived a few minutes longer...