When confronted with new shit, my original ability to tolerate it has reduced in conjunction with my age increase. Raw processing speed peaks at age 19; short term memory peaks around 25. Vocabulary peaks at older ages, but vocabulary is not typically useful for dealing with most new shit.

Some shit causes physical trauma that an older body cannot handle with grace and agility.

Retirement is near, and shit that would threaten to derail, postpone, or otherwise interrupt (i.e. by my own, premature death) that would deprive me of the payoff my age has entitled me to receive.

"Shit"s definition is no longer the same as it was when I was a younger person. Age has created in me an inability to flexibly change my internal definition of "shit", and so I have become rigid in my understanding of "shit." New "shit" is beyond my ability to process gracefully.

The ability to deal with "shit" requires energy. The amount of extra energy a body can expend in a given period of time is directly related to youth. And so, as we get older, the available energy we can expend on a situation reduces during the same period, and some shit is beyond our energy reserves