Except as provided in § 16.1-285.1, all commitments under this chapter shall be for an indeterminate period having regard to the welfare of the juvenile and interests of the public, but no juvenile committed hereunder shall be held or detained longer than thirty-six continuous months or after such juvenile has attained the age of twenty-one years. However, the thirty-six month limitation shall not apply in cases of commitment for an act of murder or manslaughter. The Department shall have the authority to discharge any juvenile or person from its custody, including releasing a juvenile or person to parole supervision, in accordance with policies and procedures established by the State Board and with other provisions of law. Parole supervision programs shall be operated through the court services units established pursuant to § 16.1-233. A juvenile or person who violates the conditions of his parole granted pursuant to this section may be proceeded against for a revocation or modification of parole status pursuant to § 16.1-291.