A lot of subcultural behavior is mocked and derided, but the fact is that subcultures produce their own language markers as shibboleths. This goes back at least 3000 years.

Yes, but that doesn't have anything to do with just age, which is what the parent was trying to assert. People do talk like this, but certainly not everyone. Outside of actual frats and sororities in colleges, this isn't common at all except in jest.