senility
耄 centers on the mental decline of extreme old age: senility, becoming forgetful and confused.
耄 combines 老 (old) and 毛 (hair), likely suggesting the thinning or whitening hair of extreme old age, which is associated with senility.
An old person (老) with thinning hair (毛) is a vivid image of senility and mental decline.
For ボウ, imagine an old person with a bow in their hair, but they've forgotten why it's there: bow -> ボウ, and the senile old person just looks confused.