Hibernation wouldn't really cut it. Hibernation doesn't stop aging, after all. There are only four types of beings that survived from the 4th world: Dragons, Immortal Elves, Infected, and Spirits. The first two are right out, so forget about them for now.
Infected - like Crimson, you're dealing with Type I Infected. If you're wanting to do Elf, then it would be a Banshee, unless something SERIOUSLY crazy (like 'early novel writers played fast and loose with the game rules' crazy) happened.
Spirit - Either the spirit is in the shape of an elf, or is Inhabiting the elf. Either way, not an elf.
Otherwise, you have to come up with a DAMN good reason why he hasn't aged in thousands of years.
Either way, you'll have to come up with some reason why the 'elf' hasn't shown up before now. Honestly, just stick to 'magical weirdness'. Something like an Alchera where time decided to stop, so that it has LITERALLY only been a couple seconds for him. (This would also solve the 'aging' issue.) There are plenty of events in recent history that could have shook the alchera loose and unstuck time: Big D's death, the Comet, Aztlan's magical pollution, the artifact hunt, the closing of the Watergate Rift, and more. Could be fallout from a dragon-battle.
You're going to have to decide just how long he's been in the modern world. If you want him to be even slightly functional, I'd say one of the earlier events, especially the Comet, would be an excellent choice. That'll have given him enough time to piece together enough about this modern world that he can actually survive without heavy assistance. There are only two languages that have survived since the 4th world (Sperethiel and Or'zet), and only one of those has been continually spoken (though not openly), but it still would have signs of drift. Even dealing with native Sperethiel speakers, your elf would be like someone speaking Old English to people in Times Square today.
Which brings up the next point. Someone like this WOULD have been heard about quickly unless someone else snapped them up and hushed it up. Crimson had only slept for a little while, not thousands of years, IIRC. So pick one of the big players. You're most likely talking about a Dragon, or one of the IEs. Honestly, you're going to be stuck being one of their agents. Take the 'Friends in High Places' quality, and go wild. Your GM will love you.
Now, where do you want to be found? If you're wanting to include Earthdawn material in your backstory, then you're looking at somewhere in Europe, since that's where Earthdawn happened. And an Elf would most likely have been from somewhere near the Blood Wood (You'd know it as Chernobyl). You could even take the Changeling quality and grab the Thorns, if you wanted. But that would make you a rather unfortunate reminder of the past to most IEs, so keep that in mind.
I keep bringing up patrons, because without a patron who has helped to educate them on the modern world, your elf would likely have been locked in an asylum if they were lucky, or a megacorp research program, if they weren't. Your patron may have even had you extracted from one of those places. Why would the big players do something like that? Well, aside from you being a wonderful brag piece to show off to their friends as being a unique part of their collection, you would also know a LOT about the 4th world, information that the big players have purposefully NOT spread. And they are not keen on that info spreading without their 'guidance'.
