My last couple years of secondary school (late 90's, age 15-16), they started to introduce a little bit of mental health and sex education. It was pretty fumbling and confused - I felt terrible for the teachers trying to deliver it, and I don't think the students really got much out of it. I'm afraid I don't know how that's progressed here in New Zealand since then, although I hear that sex education starts much earlier now, around age 12 I think. Whether mental health issues are covered, I have no idea.
I definitely agree, wholeheartedly, that some basic mental health education should be included. I think it would make sense for it to be a mandatory class for people starting secondary school, even if only for a term, maybe leading on to more in-depth electives later on. It certainly would have helped me, I think. I've suffered from avoidant personality disorder since, I think, well before that time, but I suspect it would have been less severe, led to less depression, self harm and substance abuse, and that I would have understood it and sought treatment much earlier, if I'd had some education about mental health issues back then.