No disagreement: it’s a reference to Ancient Greek pederasty. Being a classical reference, it would have a classicist, learnèd origin: it’s not a turn of phrase some random peasant on the Loire came up with.
Aller se faire voir chez les grecs says that the expression is no early than the start of the 20th century. The whole “Greeks were pederasts trope” would have been pretty firmly entrenched by then; the use of classical references to conceal obscenities among the intelligentsia would have been well established by then too.
I don’t see the expression being 18th century; just skirting too close to taboo. But what do I know. Y a-t-il un spécialiste de linguistique française qui sait nous dire plus?