1) An oldster in his dotage 2) Doater 3) Feeble fellow 4) Foolish chap 5) Golden ager 6) Graybeard 7) Not the brightest oldster 8) Old person 9) Old-timer 10) Older person 11) Oldster 12) One in a second childhood 13) One in second childhood 14) One way over the hill 15) Senile one 16) Senile sort 17) Senior citizen 1) Dodo 2) Veteran 
• (v. i.) One whose mind is impaired by age; one in second childhood.
Do'tard noun [ Dote , intransitive verb ] One whose mind is impaired by age; one in second childhood. « The sickly dotard wants a wife.» Prior. 
[n] - an oldster in his dotage
noun an oldster in his dotage; someone whose age has impaired his intellect
a person, esp. an old person, exhibiting a decline in mental faculties; a weak-minded or foolish old person. · doater.
someone whose age has impaired his or her intellect