Per Yahoo UK: You can start referring to others as senior when they're about 55.....
Per wikianswers.com: How old do senior citizens have to be? At least 62.
Per phoenixabout.com: How old is a senior? 62+.
Per legal-dictionary.thefreedictionary.com: Senior citizen = Elderly persons, usually more than sixty or sixty-five years of age.
Per dictionary.reference.com: Senior citizen = an elderly or aged person, especially one who is retired or whose principal source of support is a pension or Social Security benefits.
