Ought vs is.
World should move towards what is ought as that describes what should be, rather than what it is. If you only support is, nothing will change.
Off course, directly breaking law is stupid till law is changed.
Btw, sexual maturity can be seen just by looking at person, so it's easier to know. If you think other people will disagree did specific person reach sexual maturity, it's too young.
Also, someone can be of legal age/age of consent/whatever and still belong into category don't sleep. Why? Delayed puberty, sex hormones issues. See, that why ought should be used.
EDIT: As general rule avoiding usage of bureaucratic criteria is very good. Don't allow rules written by consquence-avoidance-people (ie bureaucrats) to override your common sense.
If something is stupid, it's stupid even if written as law. Breaking law is special topic always btw.