Final answer:
Normal changes in cognitive processing often start in people's mid-50s. Engaging in mental and physical activities can mitigate this decline.
Step-by-step explanation:
According to research on cognitive development, normal changes in overall cognitive processing begin in people on average in their mid-50s.
While our crystallized intelligence, which includes knowledge and skills we've accumulated over a lifetime, remains steady or even improves with age, another aspect, our fluid intelligence, which encompasses information processing abilities, reasoning, and memory, may begin to decline in late adulthood.
Engaging in mental and physical activities can help delay the onset of cognitive decline and reduce the incidence of mild cognitive impairment and dementia.