One way to categorize waves is to say that there are longitudinal and transverse waves. In a transverse wave, particles of the medium are displaced in a direction perpendicular to the direction of energy transport. In a longitudinal wave, particles of the medium are displaced in a direction parallel to energy transport.
Seven plans allowed normal retirement within these ages. Six of them required at least 30 years of service for normal retirement. Only two of the plans continue to allow normal retirement within these ages. Both now require a minimum age of 57 and at least 30 years of service. For most plans the minimum age requirement increased to the range of age 60 to age 62. Age 60.
Members of Congress may retire with full benefits at age 62 after five years of service, at age 50 after twenty years of service, and at any age after twenty-five years of service. They may retire with reduced benefits at ages 55 to 59 after five years of service, and age 50 after 20 years of service.