Other forms: dotages
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).