25% of Canadians are no longer virgins by 12, which means that 12 is too late to start discussing it for 25% of the audience.
I started talking to my kids about it when they were about 5, and made it a policy to answer any question they asked at the level of detail they asked, with the exception of personal details in my own sex life. I think it worked out pretty well, even if it wasn't exactly comfortable. Did have to say to one of my now-married kids that I'm happy they have a healthy sex life, but I'd prefer the sex paraphernalia not be left in the common areas when we stop by.
Pretty accurate. You have no idea how many minutes there are in the third hour after midnight when your kid won't stop crying.