wrinkled face of the elderly
耇 centers on the visible signs of advanced age, specifically a wrinkled face. It describes the elderly appearance itself rather than abstract old age.
耇 combines 耂 (old) with 句, which likely contributes a phonetic element. The character is associated with the wrinkled appearance of the elderly, but the exact historical development is uncertain.
The top 耂 suggests an old person, and the bottom 句 looks like a bent, wrinkled shape. Picture an elderly face with deep wrinkles, like the lines of 句 etched into the skin.
For コウ, imagine an elderly person with a wrinkled face coughing (コウ) from age: the cough sound cues コウ while the wrinkles show their years.