Oldest in both terms is Nico, more or less. She started out as a straight-up self insert. Then I tweaked her a bit and removed her "origin". Then I tweaked her a bit more and she grew from that.
Youngest-by-age, I really couldn't say, because, even when I exclude the immortals, for some of them I have ideas for stories spread over decades... The youngest I've written may have been Sylvie in Perception. Or, for a given value of "character", the kids in Family Values.
Youngest-by-time-made-up: There's Ardí from "Perception", about whom I know very little, but who now is part of Eodea-canon and thus I guess will show up again some time (anything that saves me coming up with another name). (Eralai is sort-of older; the name and fact she had something to do with Sylvie's schooling are from an offhand mention in 2007.)
Or Vickie, who showed up in a pair of VSSs, and might be good for a bit of Flash Fiction.
