senior citizen

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A person of relatively advanced age, especially one who has retired.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An old person; generally, a senior citizen is considered to be over sixty years of age.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an elderly person