I'm in my early forties and I can remember having my first boyfriend in 6th grade......talking on the phone, went to the skating rink together, all innocent enough. By fifteen I had a boyfriend that I dated until I was twenty.
I agree with the other posters in that you are the best judge of what your kids should and shouldn't do.
With my sons, however, I have discouraged it. DS(almost 15) just went to the movies for the first time with a girl he liked. They text each other and talk but between their schedules there hasn't been much opportunity to see each other often (and I'm secretly kind of happy about that). DS13 is still immature in many ways and girls (other than purely friends) aren't even on his radar yet.
I've seen through some of their friends (and those friend's FB pages) that by about 7th grade the whole dating game becomes this big deal. And it just seems like the kids are in such a hurry to be grown-up, doing grown-up things (we're so in love). I'm in no hurry for that and won't encourage it. One of DS13's friends just broke up with his girlfriend of 8 months and I'm currently watching all of that drama unfold via FB and I can't stop thinking that these are 12/13 year old kids trying to replay the adult break-ups they see on tv.
To each their own, I just know for myself, I'm not really looking forward to all of the drama that goes along with it, and as the kids get older, a whole new set of issues presents itself. I encourage them to have friends, male and female, and just have fun and live in the moment of being kids. They've got their entire lives for dating and relationships.