Scientists have long believed that our ability to think quickly and recall information, known as fluid intelligence, peaks around age 20 and then begins a slow decline. However, a recent study from neuroscientists at MIT and Massachusetts General Hospital (MGH) suggests that different components of fluid intelligence peak at different ages, some as late as 30—and other cognitive skills appear to peak
even later in life.

“At any given age, you’re getting better at some things, you’re getting worse at some other things, and you’re at a plateau at some other things. There’s probably not one age at which you’re peak on most things, much less all of them,” says Joshua Hartshorne, a postdoc in MIT’s Department of Brain and Cognitive Sciences and one of the paper’s authors.

“It paints a different picture of the way we change over the life span than psychology and neuroscience have traditionally painted,” adds coauthor Laura Germine, a postdoc in psychiatric and neurodevelopmental genetics at MGH.

Hartshorne and Germine developed a new way to analyze old data sets on adult performance at different ages on the Weschler Adult Intelligence Scale, which is used to measure IQ, and the Weschler Memory Scale. This analysis revealed that performance on different tasks—such as memorizing numbers, searching for visual elements, and assembling puzzles—peaked at all different ages.

To verify their results, the researchers turned to experiments on the Internet, which makes it much easier to recruit a huge pool of subjects of all ages. Their websites, Gameswithwords.org and ­Testmybrain.org, feature cognitive tests designed to be completed in just a few minutes.

After studying data from nearly 50,000 subjects, the researchers found a very clear picture showing that each cognitive skill they were testing peaked at a different age. For example, raw speed in processing information appears to peak around 18 or 19 and then immediately starts to decline. Meanwhile, short-term memory continues to improve until around age 25, when it levels off, and then begins to drop around 35.

The ability to evaluate other people’s emotional states seems to peak much later, in the 40s or 50s. And while earlier data had shown that crystallized intelligence—the accumulation of facts and knowledge—peaked in the 40s, a vocabulary test found that it is now peaking in the late 60s or early 70s, perhaps because of increases in education, reading-­intensive jobs, and opportunities for intellectual stimulation later in life.

More work is needed to explain these results, but previous studies have hinted that genetic changes or changes in brain structure may play a role.