Multiphoton microscopy was employed for monitoring the structure changes of mouse dermis collagen in the intrinsic- or the extrinsic-age-related processes in vivo. The characteristics of textures in different aging skins were uncovered by fast Fourier transform in which the orientation index and bundle packing of collagen were quantitatively analyzed. Some significant differences in collagen-related changes are found in different aging skins, which can be good indicators for the statuses of aging skins. The results are valuable to the study of aging skin and also of interest to biomedical photonics.