Final answer:
Regular exercise contributes to improved cardiovascular health, increased joint flexibility, and improved cognitive function, but it does not slow down the metabolism.
Step-by-step explanation:
The research suggests that with age, regular exercise contributes to improved cardiovascular health, increased joint flexibility, and improved cognitive function. However, exercise does not slow down the metabolism. In fact, exercise can help increase metabolism by building muscle mass. So the answer is d) Slower metabolism.