The realization that people discussing "old anime" have moved on from stuff like Cowboy Bebop, Gundam Wing, or Evangelion, and now discuss stuff from the 00s like Death Note, Soul Eater, and Lucky Star.
I knew I'd get too old to recognize new celebrities but I did not expect to get too old to recognize what celebrities are famous for. every day I go "is that a new singer" and then a person born in 2007 goes "ew no they're a peeble streamer on doop" as I inch closer to the grave