It is NOT illegal for an under 16 to have sex. It is illegal to have sex with someone under 16. The law is for the protection of the minor not their persecution.
I blame Just 17 magazine. I remember it having "sex under 16 is illegal" at the top of their problem page. Missing the point big style, and possibly even encouraging a culture of victim blaming against under 16s who are coerced into sex against their will.