And yet...

The false dichotomy by which "adults" are magically different disregards the fact that brain development continues well past the age of majority. ( And yet most wouldn't argue for the disenfranchisement of 25 or 30 year olds. ) If we use the continuation of brain-development as a criterion for consent, then we can pretty-well eliminate reproduction until past the body's reproductive prime.

And never mind the fact that a large part of development isn't organic, but is experiential. Our culture attempts to stunt the opportunities of youth, and then blames them for making poor choices in areas they haven't been able to exercise.

Also there are always ramifications when there is a disjunction between actions and being able to exercise choice and live with consequences. Teens are told that their choices don't matter unless they conform to what is expected of them. And that the results of their actions won't amount to anything except as a rehearsal for adulthood. Removing choice and consequence has brought the global economy to its knees. Why shouldn't it be damaging to Teens?

When we delay "adulthood" until 18, we end up with College Freshmen who are almost incapable of living on their own and who tend to make very poor choices. And yet, throughout most of human culture and history 19 year olds have been capable of being established householders and parents.

As LGsinmyheart put it, we can't "wait" for them to be ready. Part of our problem is a modern focus on internal motivations. ( What I "feel like" doing. ) As P.J. O'Rourke pointed out in his commentary about Adam Smith's "personality," instead of "personality" they had "character;" character was a role you played until it came naturally. When we expected Teens to behave like responsible citizens, they rose to the occasion by first emulating others, and then acting as role-models in turn.

The false dichotomy also ill-serves "adults." Every single protection given to "vulnerable" children is removed from adults unless some sort of diminished capacity can be legally established. Now I'm not for making legal conservatorship too easy to declare, or a one-size-fits-all solution. But I think we ought to recognize that choices and relationships are complex at any age. There will always be disparities between any two partners. And redress for those who have been manipulated or exploited shouldn't be a function of an arbitrary natal anniversary, but of the actual circumstances which unfolded in a particular case.

Your description of the "teenager" doesn't resemble any teen I know, but very accurately describes the poor choices made by a lover I had when I was in my early 20s and she in her mid 30s. It can be tough to recognize when someone isn't looking out for their own interests, particularly when they're assuring you they are. Ageist views on consent limit our ability to act in the interest of "consenting adults."

Dante