It depends on the jurisdiction, as well as the severity of the crime. Generally speaking, minors can be tried as adults if they are accused of a serious or violent crime. In some states, such as California, a minor can be charged as an adult if they are 16 or older and have committed certain serious felonies. In other states, a minor may be charged as an adult for any felony if they are 14 or older.
In addition to age and severity of the crime, other factors that may influence whether a minor is tried in adult court include their prior criminal record and whether they have completed rehabilitation programs while in juvenile detention. Ultimately, it is up to the prosecutor to decide whether to charge a minor as an adult based on their assessment of the case and applicable laws.