Longman Dictionary of Contemporary English
Wiktionary
n. How old one appears to be based solely on mental ability and function.
WordNet
n. the level of intellectual development as measured by an intelligence test
Wikipedia
Mental age is a concept related to intelligence. It looks at how a specific child, at a specific age—usually today, now—performs intellectually, compared to average intellectual performance for that physical age, measured in years. The physical age of the child is compared to the intellectual performance of the child, based on performance in tests and live assessments by a psychologist. Scores achieved by the child in question are compared to scores in the middle of a bell curve for children of the same age
However, mental age varies according to what kind of intelligence is measured. A child's intellectual age can be average for his physical age but the same child's emotional intelligence can be immature for his physical age. In this psychologists often remark girls are more emotionally mature than boys in the tween years. Also a six-year-old child intellectually gifted in Piaget terms, can remain a three-year-old child in terms of emotional maturity. Mental age was once considered a controversial concept.
Usage examples of "mental age".
You have taken what was essentially a dead man with a dead brainand have restored enough of his earlier memories to bring him to a mental age of fourteen.
According to the records, Melody was fifteen years old, with a mental age of four.
If it takes the blood of children long enough, the mental age of the lich will drop.
It was a good arrangement for everyone, and it gave Kechara a never-ending stream of playmates who were all her mental age, even if she was chronologically six or more times older.
Doberman had nurtured her daughter in secret for five long years, and watched her change gradually from a sort of drooling zombie into something outwardly resembling a normal human being, though with the mental age of a backward child of four.
Only his real mental age of eighty one enabled him to tide through the sight.
Wensleydale gave the impression of having been born with a mental age of forty‑.
Wensleydale gave the impression of having been born with a mental age of forty-seven.
Wensleydale gave the impression of having been born with a mental age of forty.
Wensleydale gave the impression of having been born with a mental age of fortyseven.
In form and age she almost seemed a child, but the cool confidence of her tread and the way she measured all of us with a momentary peek, betrayed kilobytes of data about her mental age.
Devised by the German psychologist William Stern, what controversial measurement was originally defined as the ratio of a person's mental age to his physical age, multiplied by 100?