Far as I know, I’m older than most of the group here (I’m used to it. I’m older than a lot of people.) I think most of those abbreviations got their start long ago, in the USENET days. All the discussion about what things might mean reminded me of this (from 2014):
@compunaut If I’d graduated from High School (which I didn’t, because reasons), it would have been in 1964 (at 17), I graduated from college in 1982, because reasons. I retired on Feb 1, 2006, because reasons.
I’m not quite 70, but close enough. I’m betting it’s at least a decade in difference between our ages.