I am 56 today actually... not sure I really had a mid-life crises.
A little maybe. Growing older as a male is different than a female, for a woman it is primarily how they visually see themselves. For dudes, it is what we can't physically do anymore. How virile we are, or are not. And yes that certainly includes sex.
As a man, it is very difficult to deal with having to face physical limitations. Pisses you off.
Good example, just last weekend. The snow was melting everywhere and I noticed in the kitchen there was a small wet spot on the ceiling. Shit. So I go out and look at the roof, I see where it could be leaking. I get the ladder out, get on the roof...I fixed it.
But as I was making my way to the ladder, where you have to put one foot on the ladder and sort of spin yourself around... wasn't so ******* easy. I did it. But... I was fully aware that I lost my balance there for a moment, whoa nelly. Balance I once had in spades... I don't anymore.
That bothers me.