Children's mathematical achievement depends on their domain-specific abilities and their domain-general skills such as executive functions (EFs) and visual-spatial skills (VSS). Research indicates that these two domain-general skills predict mathematical achievement. However, it is unclear whether these skills are differently associated with mathematical achievement across a large age range. The current cross-sectional study answered this question using a large, representative sample aged 5-20 years (N = 1754). EFs, VSS, and mathematical achievement were assessed using the Intelligence and Development Scales-2. Hierarchical regression analyses were computed with EFs and VSS as predictor variables and mathematical achievement as dependent variable. We examined (non-) linear effects and interactions of EFs and VSS with age. Results indicated that EFs and VSS were distinctly associated with mathematical achievement above and beyond effects of age, sex, maternal education, and verbal reasoning. Effects of EFs were linear and age-invariant. Effects of VSS were curvilinear and stronger in adolescents than in children. Our results indicated that EFs and VSS related differently to mathematical proficiency across age, suggesting a varying impact on mathematics across age.