I was recently was interviewed by a Master’s Student about my opinions on mid-life crises.  I do not claim to be an expert, but I think the mid-life crisis is an identity issue.  Anyway, here are my thoughts
– Do most people experience a mid-life crisis? And does it affect men more than women? Or vice versa?
It is possible that everyone does… but I don’t know if it would count since many people handle the “crisis” with such grace that it does not seem to be a crisis for them.  However, I think everyone asks the questions that make a mid-life crisis what it is.
– How does a mid-life crisis affect a person both personally and professionally? 
It depends on how they handle the crisis.  If something damages the foundation of your life, it cracks everything else too – or at least shifts it.  Especially if your job is your foundation, as it is with most Americans, then yes, it will change at every level.
– How does a mid-life crisis affect the spouse/family/friends? What effect does the crisis have on others? 
Again, it totally depends on the way the crisis is navigated.  It can be a huge blessing to the family, if it means that dad decides to change his job so that he can focus more on them, or God, or being a healthier person.  If instead, he engages in addictive adolescent behavior – gambling, substances, addictive relationships, etc… it can be devastating.
– Is there a certain time frame that mid-life crisis usually occurs? How long does it generally last? 
As the name implies, the time frame famous for them is “mid-life”… in the late forties or early fifties.  It lasts anywhere from a few introspective moments to the rest of the person’s life.
– What signs/symptoms occur during a mid-life crisis?
a change in thinking and behavior… typically, when it is called a crisis, it is a radical change.  Often, in the stereotypical  cases, it involves a reversion to adolescent behavior – trading in the spouse for a newer model (so to speak), quitting old career, buying a red sports car, spending a bunch of money on plastic surgery, having an affair, etc.
– Does a mid-life crisis occur without warning, or are there signs leading up to it? And if there are early warning signs, are there ways to mitigate the effects? 
What is needed is identity work.  I think this is the first stages of Erikson’s crisis of “Generativity versus stagnation” – do i spend the rest of my life investing my treasure back into myself or do I spend it on others and creating a legacy? Signs would be the more minor expressions of this showing – questioning their value and purpose in life.
*** You did not ask me what I thought a mid-life crisis is.  I think a mid life crisis is the psychological bind that comes when people ask themselves “is this all there is?”  “is this what my life is and is going to be?”  “Am I ok with finishing my life on the same trajectory that I am on?”
This is mainly a crisis bc people wait until too late to ask these questions… and deny asking them as long as they can.  Well-actualized people ask these questions often (I have an alarm set on my calendar to ask them every week for me).
We need to ask these questions regularly – healthy to question.  “The un-evaluated life is not worth living”  and all that.  we encourage people in our culture to found their identity in performance and acquisition… both of which are very poor foundations… tragically so.  At one point, men aged 65-75 were the number age range at risk for suicide… like Robin Williams – what is the point of life when you cannot perform anymore?
For some more interesting info about mid-life crises, check out this informational link.