Cognitive Science

Average IQ by Age

How cognitive abilities develop, peak, and change across the entire human lifespan.

Last reviewed: February 2026

Based on cognitive psychology research

How Does IQ Change With Age?

Average IQ by age follows a well-documented developmental pattern: cognitive abilities develop rapidly in childhood, fluid intelligence peaks in the mid-20s, crystallized intelligence grows through middle age, and processing speed gradually declines after 65. IQ scores are age-normalized, meaning 100 is always the average for any age group.

Average IQ by Age: Children (5-12)

5-12 years · Avg IQ: 100 (age-normalized)

IQ testing in children measures cognitive development relative to age-matched peers. The average IQ for children is 100 by definition, as IQ scores ar...

IQ scores in children are age-normalized, meaning 100 is alw...Test-retest reliability improves significantly after age 6...

Average IQ by Age: Teenagers (13-17)

13-17 years · Avg IQ: 100 (age-normalized)

Teenage IQ scores reflect a period of significant cognitive development. Fluid intelligence peaks during late adolescence, while crystallized intellig...

Fluid intelligence (abstract reasoning, pattern recognition)...IQ scores measured at age 14-16 correlate approximately 0.85...

Average IQ by Age: Adults (18-65)

18-65 years · Avg IQ: 100 (age-normalized)

Adult IQ scores reflect the interplay between fluid intelligence (which peaks in the mid-20s and gradually declines) and crystallized intelligence (wh...

Fluid intelligence peaks between ages 20-25 and gradually de...Crystallized intelligence (vocabulary, general knowledge) co...

IQ and Aging: Cognitive Changes After 65

65+ years · Avg IQ: 95-100 (age-adjusted)

After age 65, cognitive changes become more pronounced but vary enormously between individuals. Processing speed and fluid intelligence show the most ...

Processing speed declines by approximately 20-30% between ag...Crystallized intelligence (vocabulary, general knowledge) re...

IQ by Age: Summary Table

Age Group	Age Range	Average IQ	Fluid Intelligence	Crystallized Intelligence
Children	5-12 years	100 (age-normalized)	Developing rapidly	Building foundations
Teenagers	13-17 years	100 (age-normalized)	Approaching peak	Accelerating growth
Adults	18-65 years	100 (age-normalized)	Peaks mid-20s, gradual decline	Grows through 60s
Seniors	65+ years	95-100 (age-adjusted)	Significant decline	Remains stable into 70s-80s

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Important note: IQ scores are statistical measures of cognitive ability relative to age-matched peers. They are influenced by many factors including education, health, motivation, and testing conditions. A single IQ test score should not be used as the sole basis for important life decisions. This content is for educational purposes and is not a substitute for professional psychological assessment.