Average IQ by Age: How Cognitive Ability Changes Over Time

Does IQ change with age?

This is one of the most frequently asked questions about intelligence, and the answer is more nuanced than a simple yes or no. Different aspects of cognitive ability follow different trajectories throughout life. Some decline with age, some remain stable, and some actually improve well into adulthood.

The key distinction is between fluid intelligence and crystallized intelligence — a concept first articulated by psychologist Raymond Cattell in the 1960s. Understanding this distinction is essential to making sense of how IQ relates to age.

Fluid intelligence peaks early

Fluid intelligence — the ability to reason abstractly, solve novel problems, and recognize patterns — reaches its peak in early adulthood, typically around age 20-25. After this peak, it begins a gradual decline that continues throughout the lifespan.

Research by Joshua Hartshorne and Laura Germine, published in 2015 in Psychological Science, analyzed data from tens of thousands of participants and found that different components of fluid intelligence peak at different ages. Processing speed peaks earliest, around age 18-20. Short-term memory peaks around age 25. The ability to evaluate other people's emotional states doesn't peak until the 40s or 50s.

The decline in fluid intelligence is not dramatic in healthy individuals. A person in their 60s may score somewhat lower on pattern-recognition tasks than they did in their 20s, but the difference is typically modest — perhaps 10-15 points on an IQ scale — and is offset by gains in other areas.

Crystallized intelligence grows with age

Crystallized intelligence — accumulated knowledge, vocabulary, and learned skills — follows the opposite trajectory. It continues to grow throughout adulthood, often peaking in the 50s or 60s. This is why older adults often excel at tasks requiring general knowledge, verbal reasoning, and experience-based judgment.

This growth makes sense: crystallized intelligence is built through decades of learning, reading, working, and interacting with the world. A 55-year-old has had 30 more years to accumulate knowledge than a 25-year-old, and this advantage shows up clearly in tests of verbal ability and general information.

Average IQ scores by age group

Because modern IQ tests are age-normed, the average IQ for any age group is always 100. Tests are specifically designed this way — your score reflects how you compare to others your age, not to the general population. This means that a 70-year-old and a 20-year-old who both score 100 have each performed at the average level for their respective age groups.

However, raw cognitive performance does vary by age. If we were to compare raw scores across age groups without age correction, we would see the following patterns:

Ages 16-19: Raw performance on fluid reasoning tasks is near its peak. Processing speed is at its maximum. Vocabulary and knowledge are still developing but show rapid growth.

Ages 20-34: This is the period of peak overall cognitive performance for most people. Fluid reasoning remains strong, and crystallized knowledge is growing rapidly. This age group typically shows the highest raw scores on comprehensive IQ tests.

Ages 35-54: Fluid reasoning begins to show modest declines, but crystallized intelligence continues to grow. Net performance on most IQ tests remains stable or slightly improved, as gains in knowledge compensate for losses in processing speed.

Ages 55-69: Processing speed declines more noticeably. Working memory shows some reduction. However, vocabulary, general knowledge, and verbal comprehension often remain strong or continue to improve. Performance on timed tests may decline while untimed measures hold steady.

Ages 70+: Both fluid and processing speed measures show more significant declines. Crystallized intelligence begins to plateau or decline slowly. However, many individuals maintain strong verbal abilities and practical reasoning well into their 80s and beyond.

The Flynn Effect and generational differences

One factor that complicates age comparisons is the Flynn Effect — the observation that average IQ scores have increased over time, roughly 3 points per decade throughout the 20th century. This means that a 25-year-old in 2020 might score slightly higher on the same test than a 25-year-old in 1990, not because individuals are smarter, but because environmental factors (better nutrition, more education, more cognitively demanding environments) have boosted test performance.

Recent research suggests the Flynn Effect may be reversing in some developed countries, with scores on certain tests declining slightly. The reasons for this reversal are debated but may include changes in education, technology use, or environmental factors.

Preserving cognitive function

Research consistently identifies several factors that help preserve cognitive function as we age: regular physical exercise, continued learning and mental stimulation, social engagement, good sleep, and management of cardiovascular risk factors such as high blood pressure and diabetes.

A landmark study published in the journal Neurology in 2014 found that regular exercise was associated with slower cognitive decline, equivalent to being about 10 years younger in terms of cognitive performance. The study followed nearly 900 participants over multiple decades.

Take the IQ test to see how your cognitive abilities compare across different domains.