For fans of old anime prior to 1997, definitely check out Vintage Anime Fans on Facebook.
According to the Facebook page introduction by page owner, Jarod Nandin:
Hello and welcome to the Vintage Anime Fans group.
By definition, this group should only concern anime that was created on or before 1997, however, for the sake of flexibility, we have decided to include all anime from the 20th century. Please observe the following five rules when posting here:
Rule #1: Be civil and polite in your posts and replies to this group.
Rule #2: Do not Troll, Flame, or Spam in this group.
Rule #3: Do not make posts or replies that violate Facebook’s community standards rules.
Rule #4: Do not post any links to or of illegally distributed or licensed works including, but not limited to: anime, novels, manga, etc.
(Exception: posting videos of short clips of scenes is okay)
Rule #5: Post only about Anime created on or prior to the year 1999.
(Exception: Franchises that began before 1999, such as Macross and Gundam, or remakes of vintage anime such as Astro Boy and Yamato 2199)
Feel free to post about your experiences with vintage anime, such as your favorite memories, favorite video clips, collectables, convention moments, etc. You are welcome to invite your friends and make new ones and share your love of vintage anime. We hope you enjoy yourselves.
Featuring members who worked in the anime industry during those years, fans who have attended anime cons since the ’80s and more.