Per WOJ, Angels and many of the Gods of the various religions existed prior to reality. So, the Titans of Greek Mythology, Odin, Ymir, Enki, Ra, Amun, Ptah, Gaia, Oranous, Phanes, Pontus, The Yellow Emperor of the Celestial Bureaucracy, Izanagi and Izanami, etc. Anyone involved in the a Creation myth. Perhaps more. The idea being that all of them remember Creation a bit differently and so have wildly different versions, yet all are the same story.
I think we can safely assume, given the nature of Outsiders and the familiarity of Outsiders with such powerful beings as Angels and Gods, that the Outsiders and presumably the Old Ones also pre-date Creation. In a sense, it's almost a given that the Outsiders "pre-date" reality given that from their perspective, all time would be happening all at once. Outside of time, reality would be a closed circle. Beginning and end are not really sensible terms from that perspective. To them, it's all happening all at once. Which means, wherever they enter isn't quite as important as when they enter.
So to summarise: The Creator, the Angels, some of the Gods and presumably some demons (depending on your legend), and the Outsiders and the Old Ones all pre-date Creation of Reality.
So Uriel and the Walkers are all as old as each other, at least from the Universe's perspective. From their own perspective that's a far more difficult question.
Odin, and potentially the Mothers (or whatever being(s) the Queen of Faerie are from), perhaps Hades and Ethniu (although neither were involved in Creation myths, it doesn't necessarily count them out), Laciel, Anduriel, Namshiel (and all other Denarians we have met), and all the Angels - all pre-date Reality.
Demonreach wasn't made "outside" of time, just across multiple times (and likely multiple dimensions and universes). So he at most it as old as there were people...which isn't that old really.
Ferrovax is an interesting one. Dragons supposedly were in charge of making sure things were happening the way they should, and did things like move rivers around (or start them). Serious things. Ferro could well be older than any form of life on the planet, potentially. Very hard to pinpoint. But Ethniu seemed to imply he was younger. And both were implied to be younger than Vadderung.
Drakul is almost certainly older than humanity, considering the Black Court have been around "since the dawn of humankind" or something like that. The being itself could be a lot older.
I think Lord Raith is older than Nicodemus, but I could be wrong. I seem to remember reading something about that.