The circuit court shall commit all offenders under eighteen years of age, duly convicted before the court, to the Hawaii youth correctional facilities in all cases where the court deems the sentence to be more suitable than the punishment otherwise authorized by law. In such a case, when the term of confinement ordered by the court extends beyond the offender’s eighteenth birthday, the offender shall, upon reaching the age of eighteen, be committed to the custody of the department of corrections and rehabilitation for completion of the sentence. Persons committed to the Hawaii youth correctional facilities under this section may be furloughed or paroled by the director, unless the commitment order issued by the court requires prior approval by the court or unless the offender is subject to a mandatory term of imprisonment which term has not yet expired.