Final answer:
The decline in taste that Joe is experiencing as he ages is due to the shrinking of the olfactory receptors in his brain.
Step-by-step explanation:
The decline in taste that Joe is experiencing as he ages is likely due to the shrinking of the olfactory receptors in his brain. As people get older, the ability of olfactory neurons to replace themselves decreases, leading to a condition called age-related anosmia. This loss of smell can result in food tasting bland, even when heavily seasoned. To enhance the taste of food, many elderly individuals rely on adding ingredients, such as salt, that stimulate the gustatory sense.