When in doubt, check Wikipedia! LOL Here's what it says:
Midlife crisis is a term used in [A title="Western culture" href="vny!://en.wikipedia.org/wiki/Western_culture"]Western societies[/A] to describe a period of dramatic self-doubt that is felt by some individuals in the "middle years" of life, as a result of sensing the passing of youth and the imminence of old age. Sometimes, transitions experienced in these years, such as aging in general, [A title=Menopause href="vny!://en.wikipedia.org/wiki/Menopause"]menopause[/A], the death of parents, or [A title="Empty nest syndrome" href="vny!://en.wikipedia.org/wiki/Empty_nest_syndrome"]children leaving home[/A], can trigger such a crisis. The result may be a desire to make significant changes in core aspects of day to day life or situation, such as in career, marriage, or romantic relationships.
Many middle aged adults experience major life events that can cause a period of psychological stress or depression, such as the death of a loved one, or a career setback. However, those events could have happened earlier or later in life, making them a "crisis," but not necessarily a midlife one.
[A href="vny!://en.wikipedia.org/wiki/Mid_life_crisis"]vny!://en.wikipedia.org/wiki/Mid_life_crisis[/A]