Welf. & Inst. Code, § 303

(a) The court may retain jurisdiction over any person who is found to be a ward or a dependent child of the juvenile court until the ward or dependent child attains 21 years of age.

(b) The court shall have within its jurisdiction any nonminor dependent, as defined in subdivision (v) of Section 11400. The court may terminate its dependency, delinquency, or transition jurisdiction over the nonminor dependent between the time the nonminor reaches the age of majority and 21 years of age. If the court terminates dependency, delinquency, or transition jurisdiction, the nonminor dependent shall remain under the general jurisdiction of the court in order to allow for a petition under subdivision (e) of Section 388.

(c) A nonminor who has not yet attained 21 years of age and who exited foster care at or after the age of majority, may petition the court pursuant to subdivision (e) of Section 388 to resume dependency jurisdiction over themselves or to assume transition jurisdiction over themselves pursuant to Section 450.

(d) (1) Nothing in this code, including, but not limited to, Sections 340, 366.27, and 369.5, shall be construed to provide legal custody of a person who has attained 18 years of age to the county welfare or probation department or to otherwise abrogate any other rights that a person who has attained 18 years of age may have as an adult under California law. A nonminor dependent shall retain all of their legal decisionmaking authority as an adult. The nonminor shall enter into a mutual agreement for placement, as described in subdivision (u) of Section 11400, unless the nonminor dependent is incapable of making an informed agreement, or a voluntary reentry agreement, as described in subdivision (z) of Section 11400, for placement and care in which the nonminor consents to placement and care in a setting supervised by, and under the responsibility of, the county child welfare services department, the county probation department, or Indian tribe, tribal organization, or consortium of tribes that entered into an agreement pursuant to Section 10553.1.

(2) A nonminor dependent who remains under delinquency jurisdiction in order to complete their rehabilitative goals and is under a foster care placement order is not required to complete the mutual agreement as described in subdivision (u) of Section 11400. Their adult decisionmaking authority may be limited by and subject to the care, supervision, custody, conduct, and maintenance orders as described in Section 727.

(e) Unless otherwise specified, the rights of a dependent child and the responsibilities of the county welfare or probation department, or tribe, and other entities, toward the child and family, shall also apply to nonminor dependents.

(f) The court shall assume transition jurisdiction pursuant to Section 450 over a person notwithstanding a court order vacating or dismissing the underlying adjudication pursuant to Section 236.14 of the Penal Code or Section 782 of this code.