The gods' ages are at least partially a matter of preference - in Twilight we see Odin younger at the end than he was at the beginning, and giving a rather vague and evasive answer when questioned about it. It's entirely possible that she was, in fact, a preadolescent child for many centuries before deciding to grow up a bit. (She appears in the Eddas as a young woman, but the Vikings only got closer than everyone else, they weren't exactly right about everything. Corwin's favorite example of this is that they describe Urd as a withered old crone. :)

Anyway, we know Skuld was - just barely - old enough to assume her duties as Valkyrie leader in the 1940s (I would guess she was motivated to take that step by the appalling technologically-driven slaughters of the first two World Wars), and she was still around that same age (effectively 12ish) when Gryphon first met her in the mid-2100s. When next they met, in the late 2200s, she'd advanced to mid-adolescence, and IIRC her dialogue implies that she'd done so relatively recently - perhaps because, being attuned to the future, she knew she'd been meeting him again soon.

Urd's theory is that she grows up as Earth's human race does - so she spent the entirety of the pre-spaceflight era as a child; passed through a very turbulent adolescence in the centuries when humanity was spreading boldly, but with many false starts and hilarious screw-ups, across the known galaxy; and reached vigorous young adulthood just at the point when we really started getting our shit together as one of the galactic scene's main players. Dawn of the 25th century as the beginning of Mankind's Fourth Age and all that.

In fairness, most people think Urd's a bit daft. :)

--G.
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Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Mod
Eyrie Productions, Unlimited http://www.eyrie-productions.com/
zgryphon at that email service Google has
Ceterum censeo Carthaginem esse delendam.