The underlined word that supports the conclusion that the subject is old is "creaked."
In the provided sentence, the word "creaked" is the key indicator that supports the conclusion that the subject is old. The act of leaping to one's feet is typically associated with agility and youthful energy, but the subsequent description of "His bones creaked" introduces a contrasting element. The word "creaked" implies a sound often associated with aging joints or worn-out structures.
The creaking of bones is a common experience associated with the aging process. As people grow older, the cartilage between joints may wear down, leading to friction and the production of sounds like creaking or cracking. This sensory detail provides a vivid image of the physical condition of the subject, suggesting a lack of the smooth, effortless movement typically associated with youth.
Moreover, the contrast between the dynamic action of leaping and the subsequent creaking of bones adds depth to the characterization. It creates a juxtaposition, highlighting the discrepancy between the outward appearance or action and the internal physical state. This literary device draws attention to the theme of aging, subtly revealing that the subject's outward vigor is tempered by the unmistakable signs of bodily wear and tear.
While other words in the sentence, such as "Laughed," might suggest a youthful spirit, the word "creaked" directly addresses the physical condition of the subject, providing a more concrete and specific indication of age. Therefore, within the context of the sentence, "creaked" is the word that most strongly supports the conclusion that the subject is old, offering a nuanced portrayal of both movement and the inevitable effects of time on the human body.