Mental age

Psychologists often remark that girls are more emotionally mature than boys at around the age of puberty.

[2] During much of the 19th century, theories of intelligence focused on measuring the size of human skulls.

[3] Anthropologists well known for their attempts to correlate cranial size and capacity with intellectual potential were Samuel Morton and Paul Broca.

[3] Mental age was first defined by the French psychologist Alfred Binet, who introduced the Binet-Simon Intelligence Test in 1905, with the assistance of Theodore Simon.

He created an experiment that was designed as a test to be completed quickly and was taken by children of various ages.

Binet's theories suggested that while mental age was a useful indicator, it was by no means fixed permanently, and individual growth or decline could be attributed to changes in teaching methods and experiences.

[3] Henry Herbert Goddard was the first psychologist to bring Binet's test to the United States.

[7] An individual's "deviation IQ" is then estimated, using a more complicated formula or table, from their score's percentile at their chronological age.

Binet did not believe these measures represented a single, permanent, and inborn level of intelligence.

After World War I, the concept of intelligence as fixed, hereditary, and unchangeable became the dominant theory within the experimental psychological community.

The pruning process is shown in this clip that was constructed from MRI scans of healthy children and teens. The time-lapse animation compresses 15 years of brain development (ages 5-20) into just a few seconds. Red indicates more gray matter, blue less gray matter. The changes in color from yellow/red to blue show the pruning process (source: NIMH ).
Intellectually disabled patients with 1- and 2-year-old mental ages
A 78-year-old intellectually disabled woman whose " mental condition has always been that of a child 5 or 6 years of age "