The time dependence of the diffusion eigenvalues derived from diffusion tensor imaging allows one to probe tissue microstructure. A diffusion model is required to derive inferences about the microstructure from the time dependent eigenvalue data. We applied the Random Permeable Barrier Model1 to the time dependent diffusion data to infer age related changes in skeletal muscle microarchitecture. The tertiary eigenvalue at the largest diffusion time was significantly different between young and senior cohorts. Model derived myofiber size decreased and free diffusion coefficient increased with age, though neither parameter reached significance.