Cognitive aging is a key area of research, with significant progress in understanding age-related changes in cognitive functioning. The review highlights five major questions: which cognitive abilities are affected by age, how many distinct factors influence age-related cognitive changes, whether age-related declines in average performance are associated with increased variability between individuals, what causes differences between cross-sectional and longitudinal age trends, and how to investigate the causes of age-cognition relations. Research shows that cognitive abilities such as vocabulary and general knowledge tend to increase with age, while processing efficiency and speed decline. These patterns are consistent across various cognitive and neuropsychological tests. However, cross-sectional and longitudinal studies often show different age trends, which may be due to factors like prior test experience. The number of distinct age-related influences is likely smaller than the number of variables showing age-related changes. Researchers should be cautious in interpreting age differences in specific variables without considering broader influences. Age-related declines in average performance do not necessarily correlate with increased variability between individuals, suggesting that age-related changes may reflect shifts in the overall distribution rather than increased variability. The discrepancy between cross-sectional and longitudinal age trends may be partly due to practice effects, where prior test experience affects performance. Mediation analyses and other methods are used to explore causal relationships, but they have limitations. Researchers should consider multiple methods and models to better understand age-related cognitive changes. Overall, while some questions about cognitive aging have been addressed, many remain. Future research should focus on investigating the validity of assumptions about age-related variability and the causes of discrepancies between cross-sectional and longitudinal findings. Understanding these factors is crucial for interpreting age-related cognitive changes accurately.Cognitive aging is a key area of research, with significant progress in understanding age-related changes in cognitive functioning. The review highlights five major questions: which cognitive abilities are affected by age, how many distinct factors influence age-related cognitive changes, whether age-related declines in average performance are associated with increased variability between individuals, what causes differences between cross-sectional and longitudinal age trends, and how to investigate the causes of age-cognition relations. Research shows that cognitive abilities such as vocabulary and general knowledge tend to increase with age, while processing efficiency and speed decline. These patterns are consistent across various cognitive and neuropsychological tests. However, cross-sectional and longitudinal studies often show different age trends, which may be due to factors like prior test experience. The number of distinct age-related influences is likely smaller than the number of variables showing age-related changes. Researchers should be cautious in interpreting age differences in specific variables without considering broader influences. Age-related declines in average performance do not necessarily correlate with increased variability between individuals, suggesting that age-related changes may reflect shifts in the overall distribution rather than increased variability. The discrepancy between cross-sectional and longitudinal age trends may be partly due to practice effects, where prior test experience affects performance. Mediation analyses and other methods are used to explore causal relationships, but they have limitations. Researchers should consider multiple methods and models to better understand age-related cognitive changes. Overall, while some questions about cognitive aging have been addressed, many remain. Future research should focus on investigating the validity of assumptions about age-related variability and the causes of discrepancies between cross-sectional and longitudinal findings. Understanding these factors is crucial for interpreting age-related cognitive changes accurately.