DS is only 3 and i've never cut his hair. I know so many people who've done the same thing, i don't think it's that unusual 
Every single person (and i mean every one) i've ever encountered, calls him a girl. Or asks my DD about her "sister".
I'm fully expecting people to get it wrong when he has long hair, that's just how life goes. But every single person? And he wears stereotypical "boys things" if that makes a difference.
It's like in people's minds it's far more likely for a girl to have blue clothes with tractors on etc than for a boy to have long hair (DD has wore "boys clothes" and colours and has never been mistaken for a boy)
I'm not actually bothered and i don't correct them if they're strangers, just seems like a far more frequent occurrence than i expected 