Sun light seems to rip people apart. Those people with healthy tans all the time end up looking leathery.As for the actual aging process, that is almost all genetics and environmental based. If you are rode hard and put up wet, then you'll look it too much earlier on even with good genes. But with good genes, and taking care of yourself you should look damn decent for a long time.
Drug addiction is a really bad one. Everyone has already seen the faces of meth thing. Alcoholics tend to look really old as well. One of my friends has an alcoholic mom in her 40s and she looks a lot older than my mom who is over 60. People who hardcore smoke age bad too.
