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.