You might be thinking of this:
"The children now love luxury. They have bad manners, contempt for
authority, they show disrespect to their elders.... They no longer
rise when elders enter the room. They contradict their parents,
chatter before company, gobble up dainties at the table, cross their
legs, and are tyrants over their teachers."
There's actually no reliable source for the author, but it's similar to this section of Plato's Republic, Book 4:
Socrates is quoted saying the following regarding things that he thinks have
been neglected: "I mean such things as these: when the young are to
be silent before their elders; how they are to show respect to them by
standing and making them sit; what honour is due to parents; what
garments or shoes are to be worn; the mode of dressing the hair;
deportment and manners in general. You would agree with me? Yes."
I'm thinking adults have had similar thoughts about young'ns since Adam and Eve left Eden.
Tom M.