If most of the people you know are geeks and/or autistic spectrum and/or queer, then I would expect almost everyone you know to have felt like an alien for a large amount of time. However, this is unusual compared to "regular" humans, who generally only get it during puberty, unless they've experienced trauma.

Do you know lilairen from alt.poly? I dunno if she's still active there. She does a lot of writing on the "alien"/"martian" theme.