I know Cuneiform/Sumerian is pretty up there, but if I recall correctly, it isn’t the oldest. I have this condition where I keep getting obsessed with older and older cultures, perhaps because I just like digging. xD Both physically and mentally. Also I believe the older a written language is, the more spiritual energy is tied to it, which I imagine can come in handy.
I have been looking into the runes, which (probably) aren’t as old, but it is fascinating to explore an alphabet where each character has a value/meaning beyond just a sound. There is belief that the runes developed from Etruscan and Greek. Some even believe that the the runes were first, and Etruscan and Greek developed from them.
Realizing that the Greek and Etruscan letter order (A, B, G, D / Alpha, Beta, Gamma, Delta…) is completely different to the Futhark/Futhork letter order, it occurred to me that the runes must originally have followed that same order. A bit of digging reveled that the Futhark order is a Christian innovation, dating much more recently than the earliest runic inscriptions. If the runes are returned to the ABGD order, the procession of meanings makes much more sense.