Choose the word which can be best substituted Extreme old age when a man…

Dotage is most appropriate word over here

Explanation: The best substitute should convey foolishness or weakened mental faculties occurring in extreme old age.

• Dotage — means the period of life marked by decline of mental faculties and often foolish behaviour due to extreme old age; this matches the given phrase exactly.

• Senility — denotes deterioration of mental function because of old age and is related in meaning, but is a more general term and does not emphasize the foolishness aspect as specifically as 'dotage'.

• Imbecility — refers to general intellectual weakness or idiocy and is not specific to old age, so it is not the best match.

• Superannuation — means retirement or being retired due to age (often in the context of pension); it does not mean foolish behaviour.

Therefore, 'dotage' is the best substitution for the phrase describing extreme old age accompanied by foolish behaviour.