From about 40, I found myself thinking more in terms of how much time I have left and what I can still realistically hope to achieve, rather than in terms of how long I've lived.

I was 43 when my father was diagnosed with a bad cancer that would kill him two years later (at 69).

Those things together triggered a lot of things that I think made up a mid life crisis, now I'm 48 and it seems to be getting better.