I was thinking this while reading The Canterbury Tales, which isn’t exactly the oldest I’ve read (I think that goes to Homer)
But The Canterbury Tales is just so delightful! Getting into the flow of the rhyming prose is very fun to read (I’ve just been reading the Penguin Classics Coghill translation which is fantastic)
I’ve already watched the Pasolini adaptation but I’m definitely going to revisit once I finish the book.
Dead Souls by Nikolai Gogol
I'm a huge fan of 19th century Russian literature, and that is probably the oldest book I've read in that genre.
Other than that, I think Don Quixote is super fun to read at the start, but it drags on too long to be enjoyable all the way through. But that's the oldest book out of which I got a lot of enjoyment.