His Majesty's Young Offender Institution (or HMYOI) is a type of prison in Great Britain, intended for offenders aged up to 18, although some prisons cater for younger offenders from ages 15 to 17, who are classed as juvenile offenders. Typically those aged under 15 will be held in a Secure Children's Home and those over 15 will be held in either a Young Offender Institution or Secure Training Centre. A person is a young offender until they become 18, where they will be sent to an adult prison or can remain in the YOI until they turn 21 if deemed appropriate.