Genetics and lifestyle, combined, pops into my head. I’ve known people who naturally looked great when they were younger, but did not take care of themselves as far as lifestyle–so they aged very badly.
Illness and extreme stress through job loss, as well as personal and financial issues, etc. can also contribute to the decline of a person’s physical appearance.
Although it’s very prevalent in our area of North County (and in many of the other “hot spots” mentioned) we, and most of our friends are not into “having work done,” so we try to stay on top of things through lifestyle, etc., and, so far, it’s working out well.