Step 1: Understanding the phrase.
The phrase refers to a condition of extreme old age when someone behaves irrationally or foolishly.
Step 2: Analyzing the options.
(A) Imbecility: This refers to a condition of being mentally weak or lacking intelligence, which doesn't specifically relate to old age.
(B) Senility: This is a condition associated with old age, but it refers more to the general decline in mental or physical health, not specifically the foolish behavior.
(C) Dotage: Correct — Dotage refers to the period in old age when a person exhibits foolish behavior, often due to mental deterioration.
(D) Superannuation: This refers to retirement or the condition of being too old to work, not the mental decline associated with old age.
Step 3: Conclusion.
The correct answer is (C) Dotage, as it specifically refers to old age characterized by foolish behavior.