Final answer:
Older adults typically do not experience increased joint flexibility as they age. Instead, they are likely to encounter decreased bone density, reduced muscle mass, and a decline in cognitive function.
Step-by-step explanation:
As they age, older adults will commonly experience all of the following except increased joint flexibility (b). The correct answers for what older adults commonly experience are: Decreased bone density (a), Reduced muscle mass (c), and Decline in cognitive function (d).
With aging, older adults tend to have increased frailty, including the loss of muscle mass (sarcopenia), and their bones become less dense, which is a condition known as osteoporosis. Additionally, they often experience declines in cognitive function, such as memory and processing speed, which can be further exacerbated by conditions like Alzheimer's disease. However, contrary to the claim of increased joint flexibility, the aging process generally leads to stiffer and less flexible joints because of changes such as the decrease in collagen within connective tissues.