My brother has that problem, too.
We were in town and I can't remember who we were talking to, but we were talking about school an they were like, "Oh, you're going into what next year? Grade 9, 10?" And they turned to me and they were like, "You going to be giving your litle brother a hard time, eh?"
I had to bite my lip to keep from laughing, and Andrew was like, "Actually, I just graduated. She's the one going into grade 10."
He gets that alot and it never gets old. He just claims it's because of his "boyish good looks."
I say it's because he's so freaking short and skinny! And, of course, he still wears clothes he did in, like, the 6th grade, haha. I'm suprised they fit!
But I can imagine how annoying that can get.