dotage

ポアロがEmily Brewster (a tough, uncompromising, and athletic spinster)に質問しているところです。
Hercule Poirot said gently: "You did not like her?"
"I know a bit too much about her," In answer to the inquiring looks she went on. "My first cousin married one of the Erskines. You've probably heard that that woman induced old Sir Robert when he was in his dotage to leave most of his fortune to her away from his own family"
最後の文にでてきた "dotage" は "dote" と関係がありそうに見えますが、ここでの意味とは合いません。辞書で意味を調べます。
・Collins Dictionary: feebleness of mind, esp as a result of old age: Even in his dotage, our beloved Professor Stevie still sits on the tenure committee.
・Merriam-Webster's Online Dictionary: the period of old age: the time when a person is old and often less able to remember or do things: he's now in that stage of his dotage where he has trouble remembering the simplest things
・Vocabulary.com: The noun dotage describes the mental decline that many elderly people eventually experience. Those in their dotage sometimes act silly or forgetful.
The first syllable in dotage rhymes with go: "DOE-tage." The verb dote means "to be silly" and also "to be infatuated," both of which can at times describe those in their dotage (including a renewed interest in romance that many may not have experienced since they were giddy teenagers, in love for the first time).
孫を溺愛することと関係がありそうです。自分ではまだ I am not yet in my dotage. と思っていますが、この "dotage" をまた辞書で引くようなことがあれば疑った方がよいですね。