I think there is a point here that both of you are missing. For the same reason that a boss shouldn't sleep with his employee and a teacher with his student, there is a power differential between an adult and an adolescent, even someone 14 or 15 years old, that calls into question whether they truly consent, even if they are capable of doing so. In many places, the law takes this into account. It's legal for two underage people to have sex, as long as they are not more than 2 years apart in age, for example. So a 15 year old and a 17 year old can have sex, but a 15 year old and a 24 hear old can't. That makes sense to me.