Was in class at the time, PA system and teachers told us to stop and go home. Did, got home, saw the reruns with my parents. Was some surreal crap for a child.
Just used that an an example historical watershed event, but really any of the other major happenings at the time could mark that difference between us somewhat "older" folk and those just recently (<20 years) born. Or hell, even certain sayings / teachings that no longer are applicable these days; anyone else had math teachers that told you that "you won't always have a calculator with you!" or parents that warned you about "stranger danger" both on/offline?