(FORTUNE Magazine) – The wrinkling of the largest segment of our population will mean more than middle-aged men with artificially darkened temples taking up surfing. % Marketers who for decades have lavished attention on the young will continue to pay homage to the ubiquitous boomer. The numbers tell all. The number of Americans ages 45 to 64 will jump (see chart), while those ages 25 to 34 will diminish 4.9 million, to 38.2 million by 2000. Result: Old will be cool, and marketers will need a modified approach. Says Alan Causey, senior vice president at ad agency Ammirati & Puris: ''We are liable to see less specific marketing to Generation X. But a set of common values stretches across both generations.'' For example, an ad for Reebok's Bok line of casual shoes with athletic soles headlined ''Not sensible. Just slightly rational'' tries to reach Generation Xers feeling pressured to find a job, a home, stability. But it also appeals to the boomer looking for comfortable urban walking shoes. Small solace to Xers, who accuse boomers of stealing their careers, their freedom, and their dreams of nesting. Now they can add advertising to the list.

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