The heritability of IQ increases with age, reaching an asymptote of 0.80 at 18-20 years of age and continuing at that level well into adulthood, while shared environmental influence decreases across age.

The Wilson Effect: The Increase in Heritability of IQ With Age

The Flynn Effect for fluid IQ may not apply to all ages or ability levels, with lower ability levels experiencing worsening IQ over time.

The Flynn effect for fluid IQ may not generalize to all ages or ability levels: a population-based study of 10,000 US adolescents.

Children with autism show a gradual increase in IQ as they age, with verbal IQ lagging behind non-verbal IQ, but by school age, the gap has closed and visual reasoning surpasses IQ for most.

Ability Profiles in Children with Autism

Early treatment of phenylketonuria (PKU) leads to stable IQ development after 10 years, with children having near normal outcomes.

Development of intelligence in early treated phenylketonuria

Higher IQ is associated with a delayed onset of terminal decline in cognitive abilities, such as speed and verbal ability, and a steeper decline rate in those abilities.

IQ as Moderator of Terminal Decline in Perceptual and Motor Speed, Spatial, and Verbal Ability: Testing the Cognitive Reserve Hypothesis in a Population-Based Sample Followed From Age 70 Until Death

Higher intelligence is associated with thinner cortexes and faster thinning of the brain, with the cortex continuing to develop and expand intelligence-dependently.

Changes in thickness and surface area of the human cortex and their relationship with intelligence.

Higher initial IQ scores maintain advantages throughout the study period, with low-IQ children showing higher stability over time and more likely to attend higher educational tracks.

Intellectual development from early childhood to early adulthood: The impact of early IQ differences on stability and change over time

At age 16, boys have an IQ advantage of 1.8 IQ points over girls, supporting Lynn's hypothesis that males develop higher average intelligence than females.

A longitudinal study of sex differences in intelligence at ages 7, 11 and 16 years

Healthy older adults experience age-related neuroanatomical decline, but these changes are not necessarily linked to simultaneous cognitive deterioration.

Brain aging and psychometric intelligence: a longitudinal study

IQ consistency and age show a perfect relationship, with correlations increasing with age, but no sex differences in IQ changes were observed.

IQ Constancy and Age

Increased age and decreasing IQ tend to increase variability in judgments of duration, but overall accuracy in timing tasks remains generally consistent across groups.

Age and IQ effects on stimulus and response timing

The Flynn effect accounts for at least 85% of the IQ disparity between 20- and 70-year-olds, reducing age-related decline in intelligence.

Age-related IQ decline is reduced markedly after adjustment for the Flynn effect

Adults with Williams syndrome show a stable overall IQ, but Performance IQ increases with age, suggesting that overall IQ may remain stable.

The relationship between age and IQ in adults with Williams syndrome.

Higher IQ in the first two decades of life is associated with lower rates of total mortality in middle to late adulthood.

Premorbid (early life) IQ and later mortality risk: systematic review.

Initial diagnosis may help predict IQ change in young children with developmental delays, as initial diagnosis may help differentiate between potential IQ gains and mental retardation.

Predicting IQ Change in Preschoolers with Developmental Delays

Higher childhood IQ is associated with lower risk of all-cause mortality in both men and women, with a slightly stronger effect in women and before age 65.

Childhood IQ and survival to 79: Follow-up of 94% of the Scottish Mental Survey 1947

Higher education is associated with higher later life IQ scores, but not with faster cognitive processing speed.

Education is associated with higher later life IQ scores, but not with faster cognitive processing speed.

Aspirations, socialization, and role models significantly impact earnings at ages 35 and 53, while IQ has smaller but still significant effects.

IQ, Academic Performance, Environment, and Earnings

Childhood IQ's can predict adult education and occupational status, but not long-term predictions for individual normal children.

Childhood IQ's as Predictors of Adult Educational and Occupational Status

Longer education is associated with increased cortical thickness in older adults, but these associations may be overestimated when accounting for childhood intelligence.

Explorer Associations between education and brain structure at age 73 years , adjusted for age 11 IQ

Some studies suggest IQ increases with age in specific conditions like autism and early-treated PKU, while other studies indicate that the heritability of IQ stabilizes in adulthood and the Flynn Effect may not apply uniformly across all ages.