From Longman Dictionary of Contemporary Englishsenior citizenˌsenior ˈcitizen ●○○ noun [countable] OLD/NOT YOUNGsomeone who is over 60 years old or who is retiredFrom Longman Business Dictionarysenior citizenˌsenior ˈcitizen noun [countable] someone over the age of 65, usually someone who has finished their working life