California Family Code
A minor is an individual who is under 18 years of age. The period of minority is calculated from the first minute of the day on which the individual is born to the same minute of the corresponding day completing the period of minority.
An adult is an individual who is 18 years of age or older.
(a) The use of or reference to the words "age of majority," "age of minority," "adult," "minor," or words of similar intent in any instrument, order, transfer, or governmental communication made in this state:
(1) Before March 4, 1972, makes reference to individuals 21 years of age and older, or younger than 21 years of age.
(2) On or after March 4, 1972, makes reference to individuals 18 years of age and older, or younger than 18 years of age.
(b) Nothing in subdivision (a) or in Chapter 1748 of the Statutes of 1971 prevents amendment of any court order, will, trust, contract, transfer, or instrument to refer to the 18-year-old age of majority if the court order, will, trust, contract, transfer, or instrument satisfies all of the following conditions:
(1) It was in existence on March 4, 1972.
(2) It is subject to amendment by law, and amendment is allowable or not prohibited by its terms.
(3) It is otherwise subject to the laws of this state.