They're young, and they're spending.

With a taste for luxury developed through flash-sale websites, Gen Y shoppers are increasing their spending at full-price online luxury retailers more than any other age group, according to a new report.

Gen Y spent 31% more in 2011 than the year before, followed by Gen X buyers, who shelled out 23% more, according to American Express Business Insights data released during Mercedes-Benz Fashion Week. Gen Y is comprised of individuals age 18 to 29.