Only once every decade or so, a new cast of characters sweeps into TV commercials and gives the viewing public a more telling picture of the U.S. population as a whole. During the baby-booming 1950s, advertising scenes were filled with contented suburban families. By the late '60s and early '70s, those characters gave way to a groovier generation of young people. In the years following that revolution, advertisers have slavishly followed a maxim that dictates YOUTH SELLS. In TV commercials, young people seemed to be the only ones driving cars, taking vacations and buying insurance.
But in the late '80s, the...