At what age do children gain an understanding of the universality and finality of death?

According to many psychologists, Piaget included, the age at which children gain an understanding of the universality and finality of death is 9.

This is the time when they have matured enough to be able to comprehend that once a person dies, there is no coming back and they will never see them again. What they also understand is that death applies to everyone, and that one day, even they are going to die.