Greedling is kind of the youngest, but the original Greed is actually the third oldest. He was created after Lust and before Envy. See, Wrath is about 60 years old, and ages like a human. Greed is probably about 275. He left 100 years prior to the series, forty years before Wrath was even born. Number 12 didn't become Wrath until he was about twenty, so Greed would have been gone for about sixty years before 'King Bradley' was created. Greed didn't know about Wrath because Father didn't start the whole Wrath thing until about forty years after Greed left. The order is as such: Father, Pride, Lust, Greed, Envy, Sloth, Gluttony, Wrath, and then Greedling, unless you count both Greeds as the same person (which they kinda are). In the first anime, the Homunculi were created in a different order: Envy, Greed, Gluttony, Pride, Wrath, Lust, and then Sloth, though Wrath wasn't really awakened as a Homunculus until about eleven years after his creation.