Age appropriate Sex Ed

I was going to comment against someone else’s post but then felt that it warrants its own.

I’ll post my own thoughts in the comments but for everyone else:

When should Sex Ed begin?

How comprehensive should it be?

Is abstinence education acceptable?

And finally, I once read somewhere that teenagers are learning Sex Ed from Fan Fiction, what are peoples thoughts on this? (Sex Ed not fanfic, someone can create a separate topic for that)

Edit: So everyone who has replied so far agrees with early comprehensive Sex Ed (myself included).

The post I was referring to wanted to start sex Ed at the teen years. Would love to hear different opinions.