Who has buying power? Try the nation’s 78 million Baby Boomers.The Nielsen Co. research group advises that marketers, always in search of young customers, not overlook the Boomers, who are 46 to 64 years old.“When it comes to marketing, the focus always seems to be on youth,” reports Nielsen. “As a result, media companies focus on reaching consumers age 18-34 or 18-49, who spend, or have a key role in spending, billions of dollars every year.”