A mid-life crisis can be a serious matter. Turning forty (ish) men become aware of their own mortality and realise that they only have a limited life span left. Health worries can be blown out of all proportion, with minor ailments a sign of something serious. Constant mulling over "what ifs" dominate your mind and you can be convinced that your life is not what it should have been and could be made better if only you could think of some way. Many men are drawn towards reckless career moves or to dump their wives/partners for a younger woman or to give them space to find one.
At 44, having survived my mid-life crisis, I'd advise any man to realise that this is a natural process that is playing with their minds that most men go through. Instead of focussing on the "what ifs" of the past, they should think about how fortunate they are to have what they have right now. Our actions in life are not guided by hindsight and if our brains processed a bad decision, it was driven by the information on hand at that very moment. If the woman you are with now loves and cherishes you, don't be tempted by all of the young things that pass your eye. Instead, be inspired to build on what you have already and improve your life. As your mid-life crisis is telling you, there is only a limited amount of time left.
As for younger guys reading this, be warned. The mid-life crisis is coming for you!
Craig.