Who introduced the concept of mental age?

Concept

Mental age is a psychometric concept that expresses a person’s test performance as the age level at which that performance is typically observed.

It emerged from early intelligence scales that arranged tasks by the ages at which children generally solved them.

Application

Alfred Binet and Théodore Simon used age-graded tasks in the Binet–Simon intelligence scale and introduced the idea of mental age. Therefore, the attribution in this question is Binet–Simon.

Contrast

• William Stern later proposed the intelligence quotient as the ratio of mental age to chronological age.

• Lewis Terman adapted and standardized the Binet scale in the United States as the Stanford–Binet test.

• Cyril Burt contributed to intelligence testing and educational psychology in Britain, but he did not originate the mental-age concept.

Cross-check

The historical sequence distinguishes the contributions: Binet–Simon introduced mental age, Stern formulated the intelligence-quotient ratio, and Terman produced the Stanford–Binet revision.

Thus, Binet–Simon is the answer.