My first memory is mum ever so casually bringing up the topic of periods when I was about 11. I remember being mortified so I guess I already knew *something* but I haven't idea what or how. Probably stuff I learned from friends. She bought me a book Girl Talk which was actually quite informative and I read it several times. I was also an encyclopaedia reader and me and my friends used to look for the "naughty sex books" at the library when I was in Year 7.
I was lucky in that I didn't get my period until I was 16 so I'd had plenty of time to get information. Year 8 science was probably the most comprehensive in terms of menstruation and anatomy and I think that's where I learned everything I needed to know on that topic. My science teacher was pretty practical about the whole thing and while it was a little bit embarrassing (mostly because he was young and good looking) it was actually really informative and generated a lot of discussion (and this was in a Catholic school). We learned about and discussed sexuality in Year 9 Religious Ed and again in Year 11 Ethics.
When I got my period I told mum but was mortified at having to do so. I always bought my own pads in secret because I was too embarrassed to put them on the shopping list. God, I remember the first day of Year 7 and having to tell her that lessons were split up into "periods" and wanting to just die of embarrassment right then and there :-/
As for sex, it was never, ever discussed in my house (no wonder I'm a prude). I got all my information from magazines (Dolly and Girlfriend), friends and books. I lost my virginity a few months shy of 19 to my boyfriend and he taught me everything that I needed to know from a practical POV. I already knew the basics from conversations I'd had with friends, books and magazines.
I hope I'm more open with my kids. I find it really difficult to talk about these topics to anyone other than a few close girlfriends because I still get so embarrassed. I don't want my kids growing up like that.