To investigate age-related changes on passive muscle stiffness in healthy individuals and measure the shear modulus in different age groups. Shear wave elastography (SWE) movies of gastrocnemius medialis (GM) were collected during passive stretching induced by ankle rotation from plantarflexion (PF) to dorsiflexion (DF). A series of SWE images at ankle angles of PF 40°, PF 30°, PF 20°, PF 10°, 0°, DF 10°, DF 20°, and DF 30° were collected and shear moduli measured accordingly for analyses. Eighty-six healthy volunteers (27 children, 31 middle-aged adults, and 28 older people) were recruited. No significant difference was observed in the shear modulus between the three groups at ankle angles of PF 40°, PF 30°, PF 20°, PF 10°, and 0° (p > 0.05). The difference in the shear modulus among the three groups became significant as DF increased. At ankle angles of DF 10°, DF 20°, and DF 30°, the shear modulus was the greatest in the older group, followed by the middle-aged group and then the children group (p = 0.007, 0.000, and 0.000, respectively). Passive muscle stiffness increases with age, and the difference between age groups was pronounced only after reaching a certain degree of stretching. • The influence of age on passive muscle stiffness becomes pronounced only after reaching a certain degree of stretching. • Age should be considered when evaluating passive muscle stiffness in muscular disorders.