Whe I saw a derm about 5 years ago, he was at least 60 and he said he had only seen one case other than me and that it was a soldier who had the condition.
In my opinion I would break it down to either people picking/biting them so much it makes the lips consantly people becuase they are always trying to protect themselves which grow into crusts welded to lips ) or people who have lots of stress/depressed, and that seems to be the more flaky sypmtom where the skin flakes off everyday.
I don't think race is an issue, there's a mixed bunch of people on here.