According to Kohlberg's Moral Development Theory, ethical principles are…

Kohlberg's Moral Development Theory outlines three levels of moral reasoning: Pre-conventional, Conventional, and Post-conventional. The question specifically asks about the internalization of ethical principles, which characterizes the Post-conventional level. This highest stage involves reasoning based on universal ethical principles and individual conscience rather than societal rules or laws. Research indicates that this advanced form of moral reasoning typically emerges during adolescence and continues into adulthood, generally starting around age 13. Therefore, the correct answer is Option C (13 and above). Options A and B are incorrect because they represent earlier developmental stages where moral judgments are primarily based on avoiding punishment (Pre-conventional) or adhering to social norms and laws (Conventional), rather than internalized ethical principles. Option D is too young for any significant moral reasoning development beyond basic obedience.