Say you were 18, and that no longer applies.
By the time you've graduated high school, you're no longer making fart jokes...
I'm curious as to why he opted to portray the yearbook in this way
That's a very improbable cognitive error, when based on the facts.
He was coached.
But interestingly, that also means he was coached to perjure himself, as that yearbook clearly is not from when he was 16.
One typically jokes about farts after they have already passed, (pun intended)... as a way to deflect from the unpleasantness
It seems to usually be a way of forcing someone to experience something unpleasant, thusly controlling a situation. Familiar?
Because that's something darker than an innocent mistake.