Age Amnesia
A disorder that usually hits when a person gets in their 40s, sometimes it can his as early as their 30s.

People with age amnesia forget that they've have ever been kids, teenagers, or 20somethings and start to criticize the current young population as if they themselves were never a child, teen, or 20something.

People suffering from age amnesia suffer from forgetting they themselves were once teens with raging hormones or noisy little bastards. This comes with a steep misunderstanding of the young, as sufferers of age amnesia have never been a child.
Middle Age Man - "Kids these days all they do is watch TV, smoke weed, and eat bad foods"

20something - "You were a hippie back then, didn't you do the same?"

Middle Age Man - "IT WAS DIFFERENT BACK THEN!"

20something - "Whatever man, you got that Age Amnesia"