What should a person do to make up for a past unpunished crime?

Suppose that a man, say when between 9 to 12 years old, committed a serious offense such as sexual assault or rape. At the time, he did not realize the effect of his actions. Now, as an adult, he is living a decent life -- meaning that he's gotten a good education, he has a good job, and he's developed good sense of ethics. He's never told anyone about this incident. It was never reported, and he was never investigated for or convicted of that offense as a juvenile. Legally, he need not report this incident to anyone. But ethically, what should he do about it? Should be disclose it to someone -- such as his family, friends, a therapist, or even the police? Should he do anything else?