I think it's better to learn about it in high school (yr 9/10) as opposed to primary school (5/6) since I remember learning about it in year 6 and all I wanted to do was block my ears. Not that I was being immature, I just felt it wasn't appropriate, and I dunno, the discussion appeared to be disgusting rather than informative for me. Though the other students who probably knew a lot of that information already just listened, and I think at that age first hearing everything is just not appealing. I mean, at that age (well for me at least), many of the students were still immature, bullied each other and didn't really think about sex, so I don't think it was needed then. Though now as mentioned, with the Internet playing more of a prominent role in a child's life, and when I was younger I didn't really use the Internet, none of us did... and the fact that we can learn a lot of the information online...
I think times have changed, and because of that, it's more necessary to have sex education at a younger age, so yeah, I think it's appropriate for year 5/6/7 to learn it. Though when I was in school... yeah no.