Who's the oldest one of all?

[Amaterasu]

A list so far, I would say, would be as follows (Oldest to youngest)

Clear Ages

Tartaros (10400)

Okor (10218)

Somerled (2500-3000)

Renji (2000)

Shang (1100)

Remilia Scarlet (500)

Adam Gaite (around 12 x 14, so 168ish)

Tom Riddle (83 - I calculated that if he was 16 in 1948 when he made his diary, he would have been born in 1932)

Vincent (60ish)

Dean Winchester (46)

Ganondorf (late thirties)

Doomguy (late twenties)

Kakashi, Jupiter, Trixie (25)

Strazio (mid twenties)

Kanda (19)

Weiss, Blake, Yang (18-19)

Ruby (16)

Jade (16)

Sasuke (14ish)

Proto Man (3)

Stewie (1)

Dark Link (Pulled to the Omniverse at the moment he began to exist)

Unclear Ages: (listed in the order according to my assumptions)

Invoker (since the beginning of time, but how "old" is the Dotaverse? Likely very, very old though)
Crowley (since biblical times, Eden. Not a clear indication either, but Eden... probably very old too)
Sans ("Couple hundred years old")
Colonel (30s or 40s ever since he was created, which is unsure as to when that was)
Gilgamesh (early thirties, maybe? But he's a half-god so he's probably older than he looks)
Arthuria (is older than what she looks like according to lore)
Enzo Matrix (3 different ages in "real", "digital" and "digital accelerated" measures)
Amaterasu (couple of months at most, if we only count her most recent incarnation)