This summary is not the rule. The rule text controls.
When a young person has an after-care plan in place, the judge has to check in on how things are going. At every judicial review, the court looks at the progress being made toward the goals set out in that plan. This helps make sure the plan is actually working and not just sitting on paper.
The court can hold these review hearings as often as needed. There's no set schedule beyond that, so the judge decides based on what the situation calls for. These reviews keep happening until the young person is either discharged from court supervision or reaches a certain age.
The age limit depends on the type of case. If the case involved a status offense (something that's only against the law because of the person's age, like skipping school), reviews can continue until the person turns 18. If the case involved a delinquency charge (something that would be a crime for an adult too), reviews can continue until the person turns 21.