An IQ of 100 represents the average at any age
IQ scores from assessments such as WAIS locate a person within a same-age norm group. An IQ of 100 is close to the average for that age whether the person is 20 or 70.
| Score | What it represents |
|---|---|
| Raw score | Performance on the task itself, such as the number correct or amount completed within a time limit |
| Age-adjusted IQ | Position relative to a comparison group of the same age |
The same age-adjusted IQ does not necessarily mean that a younger and an older adult completed the same number of items. It means that each occupies a similar position within their own age group. What IQ score bands mean explains the score and percentile scale.
Cognitive abilities change at different ages
There is no single peak age for intelligence as a whole. A study of peak performance across cognitive abilities found that the highest average results for speed, memory, visuospatial tasks, vocabulary, and other abilities were spread from the late teens into the sixties.
| Ability | Typical period of highest performance on representative tasks | Average pattern after the peak |
|---|---|---|
| Processing speed (Gs) | Late teens to early twenties | Tends to decline comparatively early in adulthood |
| Fluid reasoning (Gf) | Twenties | Unfamiliar rule and relationship tasks gradually decline |
| Visuospatial processing (Gv) | Twenties | Rotation, spatial relationship, and construction tasks tend to decline |
| Working memory (Gwm) | Late twenties to early thirties | Tasks adding manipulation or updating to storage tend to decline |
| Crystallized intelligence (Gc) | Fifties to sixties | Often grows through middle and later adulthood before declining later |
These ranges describe representative tasks, not one fixed peak for every measure of an ability.
Speed, novel reasoning, and information manipulation tend to change earlier
Processing speed changes earlier on tasks that require comparing alternatives, finding matches, or applying symbol correspondences than on simple reaction-time tasks. Under a short time limit, an older adult may understand the task accurately yet complete fewer items.
Fluid reasoning also tends to decline gradually after young adulthood, particularly when the problem is unfamiliar or several conditions must be compared at once.
In working memory, larger age differences appear when information must be reversed, reordered, or updated rather than merely held. Visuospatial processing is more affected when shapes must be rotated, parts assembled into a whole, or several spatial relationships retained at once.
Vocabulary and knowledge often grow into later adulthood
Crystallized intelligence uses vocabulary, general knowledge, and concepts accumulated through learning and experience. Because knowledge continues to accumulate, it follows a different age pattern from processing speed and fluid reasoning.
In a study of vocabulary performance from ages 18 to 89, several vocabulary tasks continued to rise until around ages 64 to 66 before declining. Crystallized ability as a whole also increased on average into approximately the sixties.
The average profile in middle and later adulthood therefore often shows accumulated vocabulary and knowledge remaining relatively stronger than rapid processing or solving unfamiliar problems. A change in processing speed should not be treated as a uniform decline in intelligence; distinguish same-age standing from the balance across abilities.
The Japanese version of BrainTypeIQ reflects the observed age trends for Gf, Gv, Gwm, and Gs in its scoring. English-language results currently use provisional scoring adapted from the Japanese version.