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.

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)