"Allowing" sexual relationships

I often discuss this topic with my boyfriend, because we disagree so much on it.

When do you "let" your children have sex?

Is there anything such as "allowing it"? Won't they do it regardless of your disapproval?

I know people who already had sex age 13/14 and talked about it to their parents and I could never imagine my future child doing these things so young. On the other hand I want to be an open and trustworthy parent and am very aware that sexual curiosity starts very early.

The question is really about acting out these sexual curiosities