The incomes of the young and middle-aged - especially men - have fallen off a cliff since 2000, leaving many age groups poorer than they were even in the 1970s, a USA TODAY analysis of new Census data found. People 54 or younger are losing ground financially at an unprecedented rate in this recession, widening a gap between young and old that had been expanding for years. The dividing line between those getting richer or poorer: the year 1955. If you were born before that, you're part of a generation enjoying a four-decade run of historic income growth. Every generation after that is now sinking economically. Household income for people in their peak earning years - between ages 45 and 54 - plunged $7,700 to $64,349 from 2000 through 2008, after adjusting for inflation. People in their 20s and 30s suffered similar drops. Older people enjoyed all the gains. The line between the haves and have-nots runs through the middle of the Baby Boom, the population explosion 1946-64. The second half of the Baby Boom may be in the worst shape of all," says demographer Cheryl Russell of New Strategist Publications, a research firm. "They're loaded with expenses for housing, cars and kids, but they will never generate the income that their parents enjoyed."