I dunno what age I was. My Mum sat me and my older sister down at the same time to have a chat about it all. So at the time that it was appropriate for my sister to know, I was also lumped in there. Presumably because my Mum couldn't be bothered with the spiel twice. xD

My Mum was pretty open about sex and all that - like Locky said, not the ins and outs, but about the entire practice of being safe etc.