We are all familiar of the constantly repeated complaint that newer generations are worse and from time to time, I came across this phenomenon in older works, but I am curious as to what the first recorded example of that phrade is
That phrase specifically? I don't know. However, that exact sentiment is expressed by the ancient Roman poet Horace around 20 BC:
Our sires' age was worse than our grandsires'. We, their sons, are more worthless than they; so in our turn we shall give the world a progeny yet more corrupt.
(Odes book III).
This Mental_Floss blog post has a rundown of 15 old complaints, mostly between the 1700s and 1800s.
There are a couple other quotations floating about on the internet, from Hesiod and from Socrates, but these have been missattributed, and I cannot find a reliable source for them, and are therefore left out.
Edit: just realized I forgot to put an actual link about Horace