12 years—adulthood; postoperational stage
The Piaget stages of development is a blueprint that describes the stages of normal intellectual development, from infancy through adulthood. This includes thought, judgment, and knowledge. The stages were named after psychologist and developmental biologist Jean Piaget, who recorded the intellectual development and abilities of infants, children, and teens.
Piaget's four stages of intellectual (or cognitive) development are:
Sensorimotor. Birth through ages 18-24 monthsPreoperational. Toddlerhood (18-24 months) through early childhood (age 7)Concrete operational. Ages 7 to 12Formal operational. Adolescence through adulthood