Final answer:
A preschool child's opinion that a taller person is older than a shorter one exemplifies 'focus on appearance', a stage where children rely on visible characteristics to make judgments.
Step-by-step explanation:
The preschool child's belief that a tall 20-year-old man is older than a short 40-year-old man is an example of focus on appearance. This cognitive tendency reflects an overemphasis on visible attributes when making judgments about others. Preschool-age children are at a developmental stage where they are beginning to understand the world around them, but can be heavily influenced by external, visible characteristics. The concept closely relates to Piaget's stages of cognitive development, and while these young children can think symbolically and engage in pretend play, they often struggle with understanding more abstract concepts such as the non-visual aspects that contribute to age.