Castro, who is part of the 2012 high school class, signed with UCLA in February, but didn't participate in fall practice after not meeting NCAA Clearinghouse requirements.
The four-star prospect took the ACT twice this fall, to achieve the necessary score.
Castro received the results of his test this weekend, and got the needed number.
He will enroll in January and be able to participate in spring practice.
Castro will be a true freshman during the 2013 season.