Welfare and Institutions Code § 1770
ARTICLE 4. Powers and Duties of Youth Authority
Every person convicted of a misdemeanor and committed to the authority shall be discharged upon the expiration of a two-year period of control or when the person reaches his 23d birthday, whichever occurs later, unless an order for further detention has been made by the committing court pursuant to Article 6 (commencing with Section 1800).