There's no particular rule regarding what place or time period a character is from.
While I assume most characters will originate from 21st century, it's possible to have characters that date back a few hundred years. So it's possible for one character to be an iphone addicted junkie, while another one could be a feudal samurai that's never seen a landline phone before, and still communicates with a letter tied to an arrow...
If you decide to go with such a character though, try to keep in mind that such characters have no memory of their past. And that others should not immediately be able to figure out (without a doubt) you're a prehistoric neanderthal. Suspicion is fine though.
I've only received one Character application at this point in time, but I feel like I should make a really important point about character personality/traits/attributes etcetc.
Important Character Application Information
I have a strong preference towards characters that can fall into a category.
In other words, most of their traits/strengths/weaknesses should all contribute to an overall image.
I don't want to know that your character is nice when they're happy, and a bitch when they're pissed... I can figure that out without it being stated.
Eg; If I'm going to make the cheerful athletic girl stereotype, it's perfectly okay to have her secret hobby be cooking. However I don't recommend you add in that she's also a bookworm, has trust issues, folds paper cranes in her spare time, and went to go compete at the chess world championships.
I fully support being creative and mixing things up, but considering the way the character sheet is setup, a character like that just seems scattered, poorly thought out, and not at all appealing.