Is a 9-year-old child who is 145 cm tall eligible to use children's tickets?

Can’t, my younger sister only uses it after she’s 14, doesn’t understand still a student, won’t use student ticket (won’t recognize student ID), non-acceptance of height check…
Can’t, my little sister won’t give it to me once she’s 14, can’t understand as a student doesn’t play with student tickets (check for student ID), unwilling to look at height…