In late adulthood, Mr. Klondike has become increasingly likely to make socially impolite remarks about other people's appearance or mannerisms. His blunt comments are most likely to indicate late life shrinkage of the lobes.

His blunt comments are most likely to indicate late life shrinkage of the frontal lobes.

Explanation:

As we age, our brains go through changes and even shrink in size. Some areas may be more affected than others and, in Mr. Klondike's case, there seems to be atrophy in his frontal lobes. The frontal lobes are responsible for controlling our judgment, memory, emotional expressions, problem solving ability, etc. As we can see, Mr. Klondike seems to have lost the ability to control his temper and keep to himself thoughts which are considered impolite. This is most likely a sign of dementia caused by the atrophy in his frontal lobes.