Okay, so Unukalhai's from the 13th world, which became the Void. The same Void that has been around since, at least, the Fifth Astral Era. Now I'm confused.

Did I miss something here? Unukalhai's really at least 1500 years old? Putting aside the question of immortality for what I'm assuming is essentially a soul that's already dead and separated from its original body, if he wanted to prevent the same catastrophe from taking place on the Source, which is where I'm assuming we are, why'd he wait that long before hopping over here? Or did he travel through time and hopping between the worlds also means time travel a la KH 3DS?