Reaction time variables are used widely in studies of human cognitive ageing and in research on the information processing foundations of psychometric intelligence. The research is largely based on biased population samples. In the present study, large (500+), representative samples of the population of the West of Scotland were tested at ages 16, 36 and 56 years on simple and choice reaction time. Participants were re-tested eight years later, at which time they also took the Paced Auditory Serial Addition Test (PASAT). We report simple and choice reaction time means and their variabilities, their stability across 8 years, and their correlations with the PASAT. Simple and choice reaction times become slower and more variable with age. Women from age 36 to 63 show more variability in choice reaction times than men, an effect which remains after controlling for mean reaction time. Reaction time differences largely account for age differences, but not sex differences, in PASAT scores.