I had the talk with mom right around age 9, right before we were taught about puberty in school. It's important to note that prior to the discussion, I already knew quite a bit about sex from overhearing older kids (on the bus, my cousins, etc.) talk about it.
Even if you don't feel your daughter is mature enough for a discussion about sex, I hope you have already had the inappropriate touch discussion.
Explanation by the tongue makes most things clear, but love unexplained is clearer. ~ Rumi