In the Hagakure, which was compiled in the 1600s, the samurai Yamamoto Tsunetomo makes many references to the overall terribleness of the current generation of youth. He says the current generation is weaker, cowardly, and not as polite as his generation was.

This is the only example I can think of off the top of my head. It definitely shows that this sentiment is not a uniquely Western phenomenon and appears to just be a global thing that every older generation experiences.

Steven Pinker has written a whole (very big) book related to this question: "The Better Angels of Our Nature". It is an excellent work. The overall message is that actually we have become increasingly law abiding and empathetic over the course of history, and the book is full of data from different studies which support that.

Your question highlights an interesting aspect of this subject - that people seem to believe that the opposite is true, despite evidence to the contrary. Pinker talks about this at some length, and partly puts it down to a collective amnesia about how awful we used to be. We'd rather forget that great granddaddy regularly whipped his slave, and focus on how student son has been caught smoking weed.

I'm about 90% sure that neither the Plato nor Hesiod quotes you have there are actual quotes from either. Wikiquote at least lists the Hesiod one as misattributed, and I can only find people saying that such a Plato/Socrates quote is either badly paraphrased or just made up.

An alternatve question might be, are there any examples in history of people believing the later generation is better?

The book "The idea of decline in western civilization" (book review), though focused on 1870 to 1970, also has a chapter with copious older examples IIRC. I do remember him making the exception for some eastern cultures that have been in relative stasis for many generations, and believe that culture will always continue to be in stasis and harmony in the future, hence the exception in the title.

This question has been removed because it violates our rules against overly broad questions. These sorts of questions, as you have seen, tend to attract only trivia.