It’s hard to find studies on this.
They’d rather make money selling them things.
The wide spread in young people’s rates of social and psychological maturation has led some researchers to propose that we think about adolescents not just in terms of their chronological age, but also their subjective age: how old they feel and act.
The concept of subjective age seems like an excuse to drop age of consent.
We already have legal age and mental age.
Agency is similar in root to age.
“How long are you going to wait before you demand the best for yourself and in no instance bypass the discriminations of reason? You have been given the principles that you ought to endorse, and you have endorsed them. What kind of teacher, then, are you still waiting for in order to refer your self-improvement to him? You are no longer a boy, but a full-grown man. If you are careless and lazy now and keep putting things off and always deferring the day after which you will attend to yourself, you will not notice that you are making no progress, but you will live and die as someone quite ordinary.
From now on, then, resolve to live as a grown-up who is making progress, and make whatever you think best a law that you never set aside. And whenever you encounter anything that is difficult or pleasurable, or highly or lowly regarded, remember that the contest is now: you are at the Olympic Games, you cannot wait any longer, and that your progress is wrecked or preserved by a single day and a single event. That is how Socrates fulfilled himself by attending to nothing except reason in everything he encountered. And you, although you are not yet a Socrates, should live as someone who at least wants to be a Socrates.” ~ Epictetus