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.
In the United States, the standard retirement age is currently 66 (gradually increasing to 67). In Canada, the OAS (Old Age Security) pension is available at 65 (gradually increasing to 67, starting in the years 2023-2029), and the CPP (Canada Pension Plan) as early as age 60. The AARP allows couples in which one spouse has reached the age of 50 to join, regardless of the age of the other spouse.