>>> Did gangs of kids ever bully and harass adults in their 20s back in the 1970s
Yup! The gangs were called 'classes' and their victims were called 'teachers'. [Written by someone who started his teaching career in the 70s!].
On a slightly more serious note, I don't think that many of the kids I taught would have gone around, with their mates, deliberately harassing adults. However there were then, as there always have been, I'm sure, a few groups/gangs who would pick on people whom they deemed to be weak, vulnerable or 'different' in some way, whether they be pensioners, gays or whoever.