I walked away about 6 months ago at the ripe old age of 34. The simple fact is you don't need to be in your 40s or 50s to experience all this. Personally I experienced many of the above physical and mental symptoms while I was there and still now feel as though I'm putting my health back together. I am still flying and still working reasonably hard, but there is a big difference between coming home tired and existing in a constant state of fatigue or "burnout". Everybody is different, but I found the constant night flights mixed with jet lag was destroying me.
So often I'd see friends after a few rosters had passed by and think "my god he looks like ****" only to realise he was probably thinking the same about me. Photos taken during my last months in the middle east show a tired shell of a man appearing years older than I actually was.
The good news is that it does get better on the outside and life isn't as hard as you think without maids etc.
No disrespect to all who decide to stay, but please take care of yourselves because no one else will.