In section 23(5) of the [1969 c. 54.] Children and Young Persons Act 1969 (as substituted by section 60 of the [1991 c. 53.] Criminal Justice Act 1991) (conditions for imposing a security requirement in case of young persons remanded to local authority accommodation), for the words “young person who has attained the age of fifteen” there shall be substituted the words—
(a)“person who has attained the age of fourteen”;
(b)“person who has attained the age of thirteen”; or
(c)“person who has attained the age of twelve”;
but no substitution may be brought into force on more than one occasion.