The discussion I remember was from a movie-oriented person... PJ? Philippa Boyens? Not sure. Anyway they thought that the Hobbits were basically Edwardian, and then time moved "backwards" as you progressed East and south. Bree was 1900s; Rivendell was Renaissance or so; Lorien & Mirkwood bordered on Medieval? Rohan was essentially Anglo-Saxon (so I'm thinking 1000-ish) and Gondor was, well, I guess about the same only a different culture(Italian maybe? Who knows.) Dwarves I'm not sure.
I don't know if there is wide agreement on that, but it made fairly good sense to me.
On the other hand, I traversed Middle-Earth before I learned European histories and customs, so in a way, Middle-Earth makes more sense to me than Europe does.
For RPGs I guess I rely on gut instinct; how helpful can I be!
