Age distribution in a Kenics static micromixer is studied by mean age solution of a steady transport equation. The spatial distribution of mean age reveals locations of older material that could potentially cause process fouling and product defects. At the microscales of the mixer, both convection and diffusion strongly affect age distribution. A method is developed to compute an average effective diffusivity to measure False diffusion due to numerical errors. The range of Peclet number is found so that the scalar solution is not affected by false diffusion. The effect of convection and diffusion is studied for Re numbers that cover the full range of laminar flows in the mixer. Diffusion broadening is found to have a strong effect on the striation structures in the mixer. Age distribution in the mixer is quantitatively measured with a frequency distribution function and two different variances, the variance of residence time and the variance of mean age. It is found that the mean age variance decay rate increases almost monotonically as Re increases. It is shown that the distribution of mean age is always narrower than that of residence time.