AGE AND SEX DIFFERENCES IN COGNITIVE PERFORMANCE AMONG HEALTHY YOUNG ADULTS: EVIDENCE FOR DOMAIN-SELECTIVE, EARLY-ONSET FLUID DECLINE

Abstract

Cognitive decline is well documented in older populations, but it remains unclear whether measurable age-related differences exist within a much narrower, healthy young-adult range, and whether such differences are uniform across cognitive domains or specific to some abilities but not others. Using data from 1,113 participants (ages 22 to 36+) drawn from a publicly available neurocognitive dataset, we examined age- and sex-related differences across six standardized cognitive measures: cognitive flexibility, processing speed, working memory span, a fluid cognition composite, a total cognition composite, and general mental status. Because age and sex were not independently distributed in this sample, two-way ANOVAs (Age × Sex) were used throughout to isolate each effect from the other. Age was independently associated with lower scores on cognitive flexibility, processing speed, and the fluid cognition composite, with performance declining progressively across the 22–35 age range. Sex was independently associated with cognitive flexibility and the total cognition composite, with males scoring modestly higher on both. No Age × Sex interaction was significant for any measure, indicating additive rather than conditional effects. Working memory span, the total cognition composite considered as a function of age, and general mental status showed no significant age-related differences. These findings suggest that fluid and speed-dependent cognitive abilities begin to show detectable decline earlier than commonly assumed, even within a restricted and objectively healthy young-adult sample, while crystallized and composite abilities remain comparatively stable across this same window.