Completion of Piaget's Stages By the age of 15 to 20, an individual has typically entered and solidified the Formal Operational Stage . At this point, the person has reached the "highest" level of mental operations, including:
Abstract Reasoning: Thinking about concepts that aren't physically present (justice, philosophy).
Hypothetical-Deductive Reasoning: The ability to form hypotheses and systematically test them.
Metacognition: The "highest" form of thought where you think about your own thinking processes.