When I was a kid I once happened to find a book with a scientific yet popular enough comprehensive explanation of different sexual issues from anatomy through physiology and medicine to social aspects (no sexual techniques in any depth, just acknowledgment of their existence and importance) in our home library. When my mother noticed I was studying it she took it away and hid but I found it and read everything interesting stealthily but thoroughly.
A few years later she suggested I should read the book but I wasn't really interested as I knew it pretty much by heart already.
That was sufficient. I never talked to anyone about sex (except listening to friends' bullshit, of course).
1> From what age is sex education appropriate
When it becomes interesting to the child.
2> Is it the states responsibility
Of course not! Yet a formal rather than intimate introduction looks preferable to me.