"In the first survey (1989), the younger group included families headed by people born after 1954, and so was dominated by baby boomers. The latest group (2013)

"In the first survey (1989), the younger group included families headed by people born after 1954, and so was dominated by baby boomers. The latest group (2013) includes families headed by people born after 1984, and they seem not to have done nearly as well early in their careers." 1989 - 1954 = 35 2013 - 1984 = 29 I'm not particularly surprised that younger-than-29-year olds, on an average, don't earn as much, or are as successful as younger-than-35-year-olds. What am I missing here?