The period of a youth supervision and support order must not extend beyond the child's twenty‑first birthday and must not exceed—
(a) if the child is under 15 years of age on the day of sentencing—
(i) 6 months; or
(ii) 12 months, if the circumstances are exceptional; or
(b) if the child is 15 years of age or over on the day of sentencing—
(i) 12 months; or
(ii) 24 months, if the circumstances are exceptional.