The heir is subject to guardians and trustees until the time set by his father.
Read Galatians 4:2 Using Other Translations
But is under tutors and governors until the time appointed of the father.
but he is under guardians and managers until the date set by his father.
They have to obey their guardians until they reach whatever age their father set.
Scripture quoted by permission. Quotations designated (NIV) are from THE HOLY BIBLE: NEW INTERNATIONAL VERSION®. NIV®. Copyright © 1973, 1978, 1984, 2011 by Biblica. All rights reserved worldwide.
(New International Version Bible Online)