My response:
By operation of Federal law, a person who attains the age of 18 is automatically an adult, and needs no further approval from a court.
This law was enacted on March 3, 1972, as an outgrowth of the Vietnam War. It was believed, and passed as a result of the fact, that if you were old enough to be drafted and lose your life, you were old enough to Vote and be an adult, with most all other rights, duties and obligations therewith. The only exceptions are Gambling, Alcohol and Smoking. For those, you must be 21 years of age.
Prior to that date, kids were losing their lives in that War and had no say in the matter. So, the law was changed.
IAAL