How young is too young for sex ed?

England announces plans to teach sex ed in primary schools.

"We are going to think more closely about the differences between females and males, ok?"
An Introduction to Sex and Relationships, Age 7.
"Women have boobs and boys don't." "Why"
Reproduction, puberty and intercourse will be discussed by the time these pupils leave the school.
"Children are going through puberty really early on, and if you are not aware, they haven’t been to at home, or at school, and things are happening, then where’d you go?"
Their parents are kept informed but some still question when the teaching should start?
"I think it's too young for them to learn because she was asking me a lot of questions, reproduction, what is this and that. It was too much for me to answer."
Age really is an issue according to a UK-wide poll for the BBC, which found the vast majority of people believe sex and relationship lessons should be compulsory in school, but of those almost two thirds // earliest they should start is age 11.
Most people who have learnt about the basics of sex from science curriculum, but when it comes to more controversial aspects like same-sex relationships, contraception, abortion, it has been much more of a gray area. Up until now, schools have been encouraged to tackle these issues but not compelled to.
"Yeah, it's time, listen up, thank you. Look in this way."
At this secondary school, pupils say such lessons are vital.
"If we didn't have these lessons we wouldn’t know anything about abortions, or STIs or any of these, 'cause my parents don't know anything about that."
"When you talk with your parents, it just feels uncomfortable, you should 'cause that’s why people do in// lesson, cause’ you’re with your friends."
In England government ministers see the sex and relationship lessons as a way to cut the UK's high teen-pregnancy rate and spread of sexually-transmitted infections. But there are fears parents may be left without a say, over how schools deal with highly sensitive issues?
"You are removing this question/ from schools, you’re undermining parents, in fact what you are doing is taking parents out of the driving seat, and putting the state in that place."
The government has said parents values and the// of the school will be taken into account when deciding exactly how the facts of life will be taught. Sarah Campel, BBC News.