For instance: age of sexual consent, age for legally drinking alcohol, age for driving, age for voting, age for participating in pornography
Depending on the place, each of those requires a different minimum age. Why is that? Are some activities “more adult” than others? Using USA as an example: legal drinking age is 21, legal driving age is 16, age of consent varies between 16-18.
Not asking about different countries/states having different ages, but any single place having different ages for different adult activities
I’m guessing it’s because different parts of us mature at different rates. Brain development continues into the early twenties, so mind-altering substances are generally regulated with that in mind. Physical maturity ends in the late teens, so things like military service eligibility start there. Other activities are based on more abstract measures like responsibility, emotional stability, etc.