This phrase used to be associated mainly with men - the typical image was a man in his mid-forties trying to recapture his youth, often through affairs with younger women. in women we tend to think less of 'crisis' and more in terms of the natural passage of time, eg menopause. But this time can be just as hard for women as men, maybe harder.

For women, as well as the real physical and mental challenges of approaching menopause, there are often problems with a sense of losing your looks (lots of women claim to feel invisible after 40) and of course the loss of fertility can be very traumatic. Also, women at this time can have the same feelings as men about getting bored with their life, job, or relationship.

This can even be a good thing - sometimes you get the urge to start something new while there is still time!

You can find more information about this here.