Sometimes there is no requirement, but rather a recommendation.
Using the example of pornography, one can distinguish between: define adulthood at age 13.
Nach über 10 Jahren ist es Zeit, Abschied zu nehmen.
Wir möchten uns bei allen bedanken, die zum Teilen von Bildern genutzt haben.
Admission of a young person to a place may be restricted because of danger for that person, concern that the place may lead the person to immoral behavior or because of the risk that the young person causes damage (for example, at an exhibition of fragile items).
One can distinguish the legality of acts of a young person, or of enabling a young person to carry out that act, by selling, renting out, showing, permitting entrance, allowing participation, etc.
Historically and cross-culturally, adulthood has been determined primarily by the start of puberty (the appearance of secondary sex characteristics such as menstruation in women, ejaculation in men, and pubic hair in both sexes).
Your visitors can thus discuss through public and private chat rooms.
For girls, puberty begins around 10 or 11 years of age and ends around age 16.
Boys enter puberty later than girls - usually around 12 years of age and it lasts until around age 16 or 17 (Or in rare cases 18 and a half).
Thus, the base definition of the word adult is the period beginning at physical sexual maturity, which occurs sometime after the onset of puberty.
Although this is the primary definition of the base word "adult", the term is also frequently used to refer to social adults.