The current study examines change and stability of cognitive skills across life stages and delves into the factors contributing to changes in cognitive skills. Specifically, we examine the associations between cognitive skills and individual characteristics and contextual factors in a large sample of German adults aged 16-65 years (N = 2,430; PIAAC-L data). Across all age cohorts, cognitive skills were predicted mainly by a person's educational background, but they were also associated with factors related to socialisation, lifestyle and personality. The findings indicate that specific factors influence cognitive skills at different life stages. For example, personality was related to cognitive skills solely in the two younger age cohorts, whereas the impacts of contextual factors were most pronounced in the middle cohort.