senior citizen 
noun
An elderly person, especially an old-age pensioner.I am making this appeal on behalf of the little children, senior citizens and single mothers....
- I wonder how many senior citizens can increase their pensions to met inflation.
- The government seems to be moving away from the pension for senior citizens.
Synonyms
retired person, (old-age) pensioner, OAP;
old person, elderly person, elder, old fogey, dotard, Methuselah, patriarch;
North American senior, retiree, golden ager;
New Zealand superannuitant
informal old stager, old-timer, oldie, ancient, wrinkly, crock, crumbly
British informal buffer, josser
North American informal oldster, woopie
offensive geriatric
literary senex
rare retirer, pensionary