Transport equations and boundary conditions for spatial distribution of age moments in steady continuous flows are derived. Mean age is the first moment. The coefficient of variation is obtained from the second moment. Mixing-cup averaged mean age and higher moments across the exit plane are identical to the corresponding moments of the residence-time distribution. Numerical solutions for a 2-D (two-dimensional) reactor are studied and compared with those from a transient tracer equation. Agreement is excellent. Local tracer distribution function curves reveal that mean age is located on the long tail for both convection dominated short circuiting paths and diffusion dominated dead zones. Computing cost for the mean age and higher moment equations is orders of magnitude lower than that for the transient tracer concentration equation, making this mean age method an efficient tool to study mixing in steady continuous flow systems. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 2561-2572, 2010