This is not a gender thing, IME; some people open up fast, others slowly, pretty much regardless.
Oh, and tell your sister to stop being silly.
Ah, i suppose i'm only speaking on a high school level basis. Guys just don't share their personal lives because of the whole "masculinity" thing and general teenage apathy too. It also has to deal with teenage need to separate themselves from their families.
Sister? I dunno if you were being literal (i was just trying to go for the crazy, insane soap opera-esque web of family problems). But yes, i if there was a person who existed like this, they would be awfully silly.
