(French, Spanish and German graduate, living in Italy, teaching English to 12/13 yr olds and have bilingual daughter)
The sooner the better, simply as a means of getting children interested in languages, interested in communicating with others etc etc.
The British school system, by and large, is fantastic, and I defend it to the death on a daily basis. The child-centred learning, the materials, the basic equipment available and the qualifications, preparation and training, and sheer dedication of the teachers is, IMO, second to none. Here, teaching is seen as something-bright-but-not-that-bright women who have been to university do. (very generalised of course, I have met a handful of truly dedicated teachers but the majority really do seem to see it as a second-rate way of earning (very little) money.)
That said, all children here start to play around with English at nursery school and it continues, as a compulsory subject, all the way through till they finish secondary at 18/19. Very few university courses don't also have an English element, at least in the first few years.
The quality of the teaching might not be what it is in the UK. (I know English teachers here who have never set foot in an English speaking country) but what they do have here, in spades, is an acknowledgement of the importance of everyone knowing at least the rudimentary basics of a second language. I do English projects in a middle school, I'm not paid by the school, or even the Italian state, but by the EU. (projects available for the "impoverished" regions in Europe, the school decides how to use these available funds. Languages, with a native speaker are always given a priority because their importance is recognised.
I'd agree in part with, (IIRC) Cory, it's not that important per se when you start doing it, but the quality of what is done, and the "affective" dimension of it, is crucial. (I did French from 11-22, Spanish only at university, but enjoyed Spanish so much more, had such a love for the language and culture that I just didn't have for the French side of things, that my Spanish is still much better than my French)
Allowing British kids to continue where we left off (foreign languages aren't important because everyone speaks English, allowing them to stop at 14) is just plain wrong. I was the only 6th former in my school to do French and German A 'levels, I ended up being shipped to another school for German and sat in the teacher's office for my 1-1 French classes.
Anner another defender of grammar teaching here too! I think another misconception is that grammar teaching is outdated and stuffy. Pah. You can't speak correctly without it. My students do grammar every week. They might not know they're doing "grammar" but they are....(it's the teachy equivalent of hiding vegetables in pasta sauces )