It also stands for showing sign of dementia these days.

Yup. Often said by people who did things as a child that didn’t realize 90% of the other children weren’t initiating the things they are doing.

“I killed a dog. Cuz you know, I was young”

No. That’s not just ‘being young’. Most kids do not do that kind of thing.

It’s the same syndrome you get from rapists in prison. They think everyone secretly wants to rape and that they are just brave.