Part of the twenty-first century update!
It’s nice how openly people can and do talk about most things these days. If the stories my parents told us of their childhood are anything to go by, there was rarely anything intimate you talked about. Hell, my grandma wrote a letter to my mom to tell her, subtly, about safe sex. And instead of being open to questions, she referred to a book. That can hardly be called a Talk, now can it?
Openness is pretty much always better. I see no reason why you wouldn’t be able to talk to your child about how penis enters vagina, provided they are old enough to deal with those words maturely. …As maturely than your average adult, at least. Having someone to talk to about things, whatever they may be, is really valuable. Otherwise they might turn to the internet for information and advice, and who knows what they’ll find there.
Communication is vital. Good thing this age has plenty of it.