second childhood
  老年的智力衰退時期
  sec·ond childhood /ˌsɛkṇd-/ 名詞
  Child·hood n.
  1. The state of being a child; the time in which persons are children; the condition or time from infancy to puberty.
     I have walked before you from my childhood.   --1. Sam. xii. 2.
  2. Children, taken collectively. [R.]
     The well-governed childhood of this realm.   --Sir. W. Scott.
  3. The commencement; the first period.
     The childhood of our joy.   --Shak.
  Second childhood, the state of being feeble and incapable from old age.
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  second childhood
       n : mental infirmity as a consequence of old age; sometimes
           shown by foolish infatuations [syn: dotage, senility]