Adult
An adult is a person who is grown up completely. The person is already past the child stage. It is the phase after being a teenager. Once someone reaches adulthood, that person typically no longer has to take directions from a parent or guardian, but rather can make decisions for themselves.
In biology, a person is considered an adult physically when they have begun or passed through the physical puberty.[1][2] Mentally and emotionally, a person is considered a full grown adult in the early or mid twenties. A person can be at legal age at 18, yet they're still in adolescence, their minds are still developing. This is one of the reasons why a person under the age of 23 can be seen as a “child” by people over 24
In most countries, someone is legally considered an adult when he or she is older than a certain age. This is called the Age of majority. Hitting the age of majority means that you are considered old enough to make your own decisions, and not having to be taken care of by your parents or other adults. In most countries, this age is 18 years. However, it varies from ages as low as 16 to as high as 21. There are many additional laws that determine from what age a person is allowed to do something; for example, vote, drink alcohol.
There are also some cultures that says a person is an adult from an age of 12 years on, for example see Bar Mitzi. In some cultures, you're an adult when your are past puberty.[3]