We only become adults when we accept our mortality. Before that, we are all little children, playing in the sandbox, catching flies and tearing their wings off to see what happens. Most people never grow out of their childish cruelty, they just find well-sounding reasons for it, such as morality, values, virtue, success, legacy. When you lose your ability to hurt anyone for your own values or amusement, either with action or with words, you’re an adult.