Biologically, an adult is a human or other organism that has reached sexual maturity. In human context, the term adult additionally has meanings associated with social and legal concepts. In contrast to a "minor", a legal adult is a person who has attained the age of adult behavior but still be treated as a child if they are under the legal age of.
The age of majority is the threshold of adulthood as recognized or declared in law. It is the Age of majority pertains solely to the acquisition of the legal control over of license are correlated to the age of majority, but they are nonetheless legally .. “Adult” means an individual who has attained the age of eighteen years.
Just about everything in all states flips to "adult" at 18 - contracts, etc. Obviously that's not 100% universal - alcohol isn't enabled until you're 21.