Cerebral white matter exhibits degenerative changes during normal aging. Noninvasive approaches to measure these microstructural alterations would be invaluable for understanding the substrate and regional variability of age-related white matter degenerations. Recent advances in diffusion MRI have leveraged high gradient strengths to increase sensitivity toward axonal size and density in living human brains. Here, we examined the relationship between age and microstructural properties measured using high-gradient diffusion MRI. We observed an increase in apparent axon diameter and decrease in density with advancing age in the corpus callosum, with changes most pronounced in the genu and relatively absent in the splenium.