I came up with this because I learned from Tumblr that there’s apparently more than a hundred fanfics for The Epic of Gilgamesh on Ao3, and I think it’s poetic in a way how we’ve still never really gotten over the first story ever.
My answer would be Le Roman de Silence, from the early 1200s, which is about the adventures Silence, a boy who was born as a girl (that’s the author’s way of describing him)and who eventually becomes a knight. I just stumbled across it randomly but I fell in love with it after reading it the first time, and I think it’s beautiful how something 1000 years old can still be around and not have lost any of it’s capability for arousing our emotions.
That I’ve read within the last 10 years:
Mysteries of Udolpho by Ann Radcliffe (1794)
Northanger Abbey by Jane Austen (1817)
Plutarch’s Greek Lives (~1st-2nd c.) from his Parallel Lives, but I’ve only been able to get a copy that included some of the Greek ones (Theseus, Themistocles, Solon, Pericles, Alcibiades, Cimon, Aristides, Lysander, Nicias). Loved it though!
Other oldests I’ve loved but that I haven’t read in more than 10 years:
Hervarar saga ok Heiðreks (Saga of Hervör and Heidrek) (~12th c.)
Egil’s Saga (~11th c.)
Confessions of St. Augustine of Hippo (4th/5th c.)