The juvenile court did not automatically lose jurisdiction over the guardianship of the minor when he turned 18 years old. The minor was made a dependent in 2001, and jurisdiction was terminated in 2003 upon the selection of a legal guardianship with Lloyd L. as the permanent plan. Five days before the minor’s birthday, Lloyd filed a 388 petition, seeking to reinstate juvenile court jurisdiction over the minor, who suffered from developmental, medical, and behavioral problems. On the day the minor turned 18, the juvenile court summarily denied the 388 petition. Both Lloyd and the minor appealed from the order summarily denying the petition. The appellate court reversed the order and remanded to the juvenile court to address the petition on its merits. The juvenile court abused its discretion when it determined it had no jurisdiction to hear the 388 petition. While the juvenile court is precluded from initiating jurisdiction over a person who is 18, it may retain jurisdiction over any person previously found to be a dependent child until that child reaches 21. Here, the petition made a prima facie case for the exercise of that jurisdiction and for a full hearing on the petition.