David Laratta's Income for the Ages
"Households are by no means locked into the same quintile over time. Young educated households with professional skills and aspirations will typically move into the higher earning brackets during their financial life cycles. Households dependent on income from unskilled labor and service employment will not see the same financial progress over the years."
Source: http://www.advisorperspectives.com/dshort/updates/Household-Incomes-by-Age-Brackets.php