Your chain is missing at least BBSs, slashdot, and fark. My own is missing Usenet and IRC (I played with them, but didn't spend time there)

Depends, I went from BBSes to slashdot to koro5hin to reddit to kbin and do not feel old.

To me old-age begins when you feel you are past the time when you can learn/experience something new and/or new tech no longer feels exciting/interesting but scary.

I have met people in their 80s who have a younger outlook on life than some people in their 40s.