Life is change. And that is continuous, from birth to the end.
Even the rate of change, changes.
Even notice older people slow down, and babies grow up fast?
Lifes crisis only slow down culminating into the final change.
To call it a mid life crisis, one have to know the range of life as well as the rate of change.
For even puberty is a crisis. And even that is different for everyone.
Noticed this is dependent on two factors instead of one -- age. It's not only limited to those two factors though.