Answer:
A kid or child becomes a mature or at least mature enough to be an adult at the age of 18 and above.
Explanation:
An adult is a human that has reached a kind of maturity, most of the time. An adult can also be a animal who reached a certain stage in its life. In contrast to a child or kid, a legal adult is a person who has attained the age of majority and is therefore regarded as independent, self-sufficient, and responsible. There is a certain age of attaining legal adulthood, although its definition may vary by legal rights and country.
The official age to become an adult is 18, which is when most people are already physically mature. You can register to vote and pay taxes, yet that person cannot buy alcohol, the legal drinking age being 21.
