Legally, anyone 17 or younger is considered a juvenile. When a person turns 18, they become a legal adult. A lot people enjoy this time because they feel they have more freedom, and in some respects, they do. However, in addition to the fun that comes with turning 18, there are also added responsibilities. There are big differences between juveniles and adults, especially when it comes to legal matters.
If juveniles are arrested for shoplifting or graffiti, they may have to perform community service and pay some fines, but they will not be sent to prison. They would stand before a judge who would report the consequences, then they would be released back to their parents. If an adult were to be arrested, they would face a jury who would decide whether to convict them of the crime or not. If they are convicted, they would be sent to prison.
For adults, trial may not happen for quite some time. So they have two options: wait out this time in jail, or bail out and return home. Juveniles do not have this option because they are released back to their parents.