In the time when Paul wrote his letter, a minor had a similar status to a slave in terms of freedom of action.1 He was not old enough yet to make his own decisions and had to listen and submit to the instructions of another.2 Even though he had the right to inheritance (de jure), being the son of the property owner, the inheritance did not yet belong to him (de facto).3 He had to wait until he reached a certain age (determined by his father)4 before he could be freed of supervision and take full possession of the inheritance (property).5
1 I mean that the heir, as long as he is a child, is no different from a slave, though he is the owner of everything,