A three-year study of nearly 4,000 adults ranging from age 19 to 94 found that brain health can improve at any age, challenging the common belief that mental sharpness must decline as we get older. Participants spent just a few minutes a day on brain-training activities, and researchers found measurable gains across multiple aspects of brain health, including thinking clarity, emotional well-being, and sense of purpose.
Nobody that lives in the world and meets people thinks that mental sharpness must decline as you get older, only that it is common.
Usually these studies say exactly that though