Juvenile probation terms don't end when a person turns 18. An individual may remain under the jurisdiction of the Division of Juvenile Justice until the age of 25. A judge is the only one who can release a child from probation, states County of San Mateo Probation.
When someone who is on probation turns 18, the probation term doesn't expire, according to County of San Mateo Probation. If the individual commits a crime after turning 18, the juvenile probation can be terminated to open up a case for adult probation. The length of time a client can be put on probation will vary on a case-to-case basis.