Ask the Experts: Does IQ Decrease With Age?

Have you ever wondered if our intelligence naturally declines as we get older? Psychology and intelligence experts offer fascinating insights into how our cognitive abilities evolve throughout our lifespan. From leading researchers at Yale, Birkbeck, and other prestigious institutions, these specialists have studied how different aspects of intelligence change as we age. Their evidence-based perspectives reveal a more nuanced picture than you might expect, with important distinctions between different types of mental abilities.

Alan S. Kaufman has answered Likely

An expert from Yale University in Intelligence, Education

The question of how our IQs change has been researched in numerous research investigations, often using the various versions of the Wechsler Adult Intelligence Scale (WAIS), the most recent being the 2008 WAIS-IV. The results have been confirmed many times, but the research is a little tricky to conduct for two reasons: 

(A) IQs are always calculated relative to a person’s age, whether that age is 10, 15, 25, 50, 72, or 88. So 25 year olds are compared to other 25 year olds in terms of the number of items they answer correctly on any given task just as 50 year olds are compared to other 50 year olds. For every age group, the average or mean IQ is set at 100. So we can’t directly compare the mean IQs across the adult age range because—by definition—every group will average 100. 

(B) the second hitch is that different age groups differ in their education level. It is more common now than 25 or 50 years ago for people to attend college and to earn degrees. Since education is related to IQ, that variable serves as a confound in the research. If IQs go down with age, how can we be sure that any decrease is due to age rather than the lower level of education, on average, for older than younger adults? 

Both of these problems are easily handled by researchers (I have conducted a number of these investigations with my colleagues). The first thing we have to do is to find a common “yardstick” to compare adults. We can compare the performance of 70 year olds, 60 year olds, 50 year olds, 40 year olds, etc. to the norms (reference group or standards) established for young adults. 

In my research, we define young adults as about age 30 (usually ages 25-34). In that way, young adults will have an average IQ of 100 because that is the way the norms are developed. When we compare adults across the life span to young adults that will tell us how IQ changes as we get older. But first we have to take care of the inequity in education across the age range. That can be done statistically by “controlling” for education (even though many more 30 year olds graduated college and many more 70 year olds dropped out of high school, this statistical procedure controls for the age to age differences. 

Now we can compare Full Scale (global) IQs for adults of different ages. A clear decline is evident. The mean WAIS-IV IQ is 100 for ages 20-24 and is 99 for ages 25-44. Then it drops to 97 for ages 45-54, to 94 for ages 55-64, to 90 for 65-69, to 86 for ages 70-74 and to 79 for ages 75+. 

But global IQ is an amalgam of different kinds of intelligence, the most popularly studied being fluid intelligence and crystallized intelligence which together—along with abilities called working memory and processing speed—are combined to yield global or Full Scale IQ. Fluid intelligence or fluid reasoning (abbreviated Gf) reflects the ability to solve novel problems, the kind that aren’t taught in school, whereas Crystallized intelligence or crystallized knowledge (Gc) measures learning and problem solving that are related to schooling and acculturation. And they have very different aging curves. 

Gc averages 98 at ages 20-24, rises to 101 by ages 35-44, before declining to 100 (ages 45-54), then 98 (55-64), then 96 (65-69), then 93 (70-74), and 88 (75+). 

The decline with age in Gf—solving novel problems—is even more precipitous. Gf peaks at ages 20-24 (100), drops gradually to 99 (25-34) and 96 (35-44) before starting a roller coaster plunge to 91 (45-54), 86 (55-64), 83 (65-69), 79 (70-74), and 72 (75+). 

These values are just averages for the entire US population of adults, with the mean IQs for each age higher for more educated individuals. But the same rate of decline across the age range seems to occur for all adults, on average, whether they are semi-skilled workers or university professors. 

Two sources to consult for those interested: Essentials of WAIS-IV Assessment—2nd edition (Elizabeth Lichtenberger & Alan Kaufman), 2013, John Wiley publisher and IQ Testing 101 by Alan Kaufman, 2009, Springer publisher.

Ian Silver has answered Unlikely

An expert from University of Cincinnati in Intelligence, Behavioural Science, Social Sciences

Intelligence, like most psychological characteristics, is highly heritable. Habitability refers to the percentage of the characteristic that is accounted for by genetic factors. Approximately 67 percent of intelligence is influenced by genetic factors. In addition to these genetic factors, research has show that early life factors, such as household characteristics, influence intelligence. Approximately 10-12 percent of intelligence is influenced by these early life factors. An important characteristic of genetics and early life factors is that they don’t tend to change as we age. As such, if approximately 77-79 percent of intelligence is influenced by factors that don’t change as we age, it is unlikely for our level of intelligence to decrease as we age. Negative environmental stimuli (e.g., head trauma) and serious diseases, however, can result in declines in general intelligence. The influence of these factors can correlate with age but aging alone does not influence intelligence.

Nachshon Meiran has answered Uncertain

An expert from Ben-Gurion University of the Negev in Intelligence

I had to choose among the options which is why I chose “unlikely”. However, the real answer is more complex in my mind.

IQ indicates the relative positioning of an individual relative the the average. This relative positioning is extremely stable. A quite recent paper in Psychological Science (to the best of my memory) found a correlation of almost .70 between IQ at age ~11 to that at age ~90.

HOWEVER, the population averages are influenced by age. The best supported factorial model of intelligence is Carrol-Cattel-Horn model, according to which there are several specific abilities such as fluid, crystalized, auditory, visual, quantitiative, and speed. All of these abilities are explained by the general factor, g’. Now, all the specific abilities but one (crystalized intelligence) decline from age ~25-30 (i.e., the population average) – some (speed) decline quite dramatically.

Michael Thomas has answered Unlikely

An expert from Birkbeck, University of London in Psychology, Cognitive Science, Intelligence

Intelligence is usually measured by a set of tests, for instance, some about language skills, some about non-verbal skills such as solving puzzles, some about how quickly you can complete a task. Your intelligence will be the average of your scores across the tasks, compared to how well other people do. The concept of ‘general’ intelligence arises because a person’s scores across the set of tests tends to be similar. As you age, different skills change at different rates.

The fastest response times you will ever have are in your mid-twenties, but (so long as you don’t develop dementia), your knowledge of vocabulary will increase throughout your life. Into your late sixties, most cognitive skills relying on things you have learned (so-called crystalised knowledge) either increase or are pretty resilient. The speed with which you can do things can decline.

The short answer, then, is that your skills may diverge with age, but your overall intelligence can remain similar. For more information on whether IQ is fixed, take a look at the Centre for Educational Neuroscience’s resource: http://www.educationalneuroscience.org.uk/resources/neuromyth-or-neurofact/intelligence-is-fixed/

Gavin Brown has answered Uncertain

An expert from University of Auckland in Education, Psychometrics, Statistics

Previous answers have correctly shown that certain aspects of cognitive functioning decline with age. furthermore, they were correct that with continued development of crystallised knowledge the slowing of those functions is not really apparent. However, with age comes greater probability of diseases that can impact IQ. So the answer really is uncertain; it depends on your health and how and if you continue to use your mind. If you want to know how to keep your mind going, Lord Robert Winston gives excellent advice in his book. Doing puzzles — sudoku, bingo, jigsaws, etc.–will keep your mind active solving new problems; this fights mental atrophy. Diet and exercise do too.

Winston, R. (2003). The Human Mind and How to Make the Most of It. London: Bantam.

Plus, something we often forget is that people with below average IQ tend not to survive into old age as frequently as those with above average IQ. So developing your IQ as young as possible will help you age longer and better. In good health, overall IQ does not necessarily diminish–but speed of processing will.

It depends…..

Verdict: It’s Complicated – Different Mental Skills Age Differently

The experts reveal that IQ change with age isn’t a simple yes or no question. While overall cognitive ability measured against young adult standards does show decline with age, the story is more nuanced. Crystallized intelligence (knowledge and experience) often improves well into middle age and declines only gradually thereafter, while fluid intelligence (novel problem-solving) and processing speed tend to decline more rapidly after peaking in the 20s. Your relative position compared to your age peers remains remarkably stable throughout life, with childhood IQ strongly predicting later-life ranking. Lifestyle factors, continued mental stimulation, and good health can significantly influence how well different cognitive abilities are maintained. Rather than viewing aging as simple cognitive decline, we might better understand it as a transformation in our mental toolkit, with some skills waning while others continue to develop.

Find more research on cognitive aging and intelligence measurement on Consensus or check out the questions below!