When is a person considered an adult?

A person considered an adult depend cultures and rules of different countries in the world. A person is an adult when that person enough ages to work,to have GED, to marry, to get drive's license, to vote, to be a military service, and enough ages to underrest by law if a person crime. Almost countries in the world set minimum ages is 18 years old.
I think a person is an adult in fact a person can control himself or herself. There are alot of person working at ages 13 - 16 years old. A lot of person get marry before 18 years old ( in Yemen 64% girls are married before 18, and Bangladesh 81% girls are married before 18). If in the United States a person will be vote at 18 years old , but in the Germany and Austria allow 16 years old to vote, and in the Liechtenstain only voters enough 30 years old. Some countries like Spain, Germany, France, Austria set law to drink at 16 years old, while in the United States allowed drink alcohol at ages 21.
So a person considered an adult depend country where is a person living. But with me ,you are an adult if you are own yourself, it doesn't matter how old you are.