This paper analyses the relationship between corporate taxation, firm age and debt. We adapt a standard model of capital structure choice under corporate taxation, focusing on the financing and investment decisions typically faced by a firm. Our model suggests that the debt ratio is associated positively with the corporate tax rate and negatively with firm age. Further, we predict that the tax-induced advantage of debt is more important for older firms than for younger ones. To test these hypotheses empirically, we use a cross-section of around 405,000 firms from 35 European countries and 127 NACE three-digit industries. In line with previous research, we find that a firm's debt ratio increases with the corporate tax rate. Further, we observe that older firms exhibit smaller debt ratios than their younger counterparts. Finally, consistent with our theoretical model, we find a positive interaction between corporate taxation and firm age, indicating that the impact of corporate taxation on debt increases over a firm's lifetime.