Final answer:
Decreased joint flexibility is an age-related change that a nurse would look for during a mobility assessment of an older adult, indicative of changes such as sarcopenia.
Step-by-step explanation:
When performing a focused assessment on an older adult client's mobility, a nurse would consider decreased joint flexibility as an indication of an age-related change to the musculoskeletal system.
Age-related changes, such as sarcopenia, which is the loss of skeletal muscle mass and strength, lead to increased frailty and decreased mobility. Additionally, aging is associated with reduced muscle tone and stiffness of joints. Therefore, improvements in muscle strength, balance, or proprioception would not typically be expected as age-related changes; rather, these would be indicators of a well-maintained level of fitness despite aging.