What is the Japanese term for an old man/grandpa who is into anime/is otaku?


Is there a casual/slang term in Japanese for an old geezer who's a hardcore
otaku? I know terms like erojiji and such but there are more referred to old
men who are just perverted in general, but what about perverted old otaku?




Kitanai rōjin is what I have found about from your question.

It means dirty old man too if you want to translate.

