I don't think it's intentional pressure, and I don't think anyone means any harm by it but I do see it from a very young age.
It's harmless comments really. I've heard parents of young babies / toddlers describe a friend of the opposite sex as their 'girl/boyfriend'. And I think it just carries on like that. Many of my ds' friends (y2) describe themselves as having girlfriends. Ds has also been asked by adults whether he has a girlfriend yet.
Now, I'm not opposed to the boyfriend / girlfriend thing. I remember having two boyfriends at primary school (at the same time!). But I wonder if by labelling it as that kind of relationship so early on, it kind of perpetuates the myth that men and women can't just be friends. Because really, my 'boyfriends' were just that - friends who happened to be boys. I played at their houses and on the street with them, just as I did with my girl friends.
It seems that often, as soon as a boy becomes good friends with a girl there's a lot of 'ooh, is that your girlfriend then? Wit woo!' going on.
What do you think? Is it just a non-issue?