awww, Pixy, you took mine!!!!!
Yes, I would
so go out with Sirius. And not at the age he's at, because that would be a bit strange, but when he was *slightly* younger. *cough*thirteenorfourteenmaybe*cough*
Hmmm, now where would we go? Probably, like Pixy said, somewhere fun. I was never into the sappy walk on the beach thing, bouquet of roses, etc. So, probably we'd do something really spontaneous, or crazy that I wouldn't imagine myself ever doing in this lifetime. Because that's just the type of thing you do with Sirius, ya know? So like....stealing Peters stuffed teddy, and holding it for ransom for like ten pounds of candy. XD Or going for ice cream, and end up smashing it in eachothers faces. (And no, NOT licking it off.

) Or go jump into the lake at midnight while it's pouring, and we're fully dressed, so we're freezing our butts off, and laughing really hard. Or bothering everyone by singing songs at the top of our lungs with the wrong lyrics. Ya know, something crazy.
We'd mostly joke around, and make eachother laugh really hard. I imagine Sirius to be really funny, so he'd probably crack me up. I love it when someone has a good sense of humor.
And we'd probably eat something you can walk around with, like ice cream. Or fast food, because I can't imagine sitting through a gourmet dinner with Sirius.
As for a kiss? Why not?

*sigh* why couldn't they be real people?

EDIT:
now that I think of it, I'd go with Ron also if I had a chance. (Who would, of course, just so happen to look exactly like Rupert Grint. Age 12, that is. I know, I'm so picky.

)
Ron's really not the romantic type, but he'd probably get me flowers, or something corny like that, but they would be all wilted from the rain. (Yeah, I know, it's mean to him, but that's honestly how I want it.) But I would like them anyway, and I guess we would sorta walk around Hogwarts. (And I want it to be fall. NO idea why.) But we'd probably joke around and talk.
By the end of the date I imagine after waiting ages for him to kiss me, I'd have to go right ahead and do it myself, seeing as he couldn't get up the nerve to do it.
Haha, it doesn't sound romantic, but I've always loved a dork.