Some may argue that it's easy to practice good financial habits when your folks are paying the bills—but going on a spending spree is just as easy.

"It could drive more consumption," said Haji of the younger generation's propensity to live at home. (The number of 20-somethings rose by more than 25 percent during the recent recession, according to some estimates.) "These young people are using their low overhead in a positive way, perhaps trying to build up some financial security. That's exactly what we would want them to do."

Their one indulgence? Cars. Young adults' average outstanding balance on auto loans averaged $13,060, a negligible $350 less than the amount those over 32 owed on their cars. Wheels, one could theorize, may be a young person's only hope for independence while living at home.

The austerity SaveUp uncovered could have other causes. For one thing, it might be that the cohort that graduated with record levels of debt into the worst job market in two decades has simply not been allowed to bury itself any deeper.



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As the New York Fed put it in a recent report on the decline in the number of under-30s carrying debt, "Consumers with substantial student debt may not be able to meet the stricter debt-to-income ratio standards that are now being applied by lenders."

But SaveUp's data track well with other studies of the millennials' saving and spending habits, and suggest the recession has had a profound impact on their attitudes toward money. In a survey conducted during the period of their study, the site found that younger users considered saving their top financial goal.

What's not clear is how they plan to use their cash.

Though millennials tend to use online financial apps more than 40-somethings, SaveUp's snapshot showed nothing conclusive about their investing or retirement planning, or their appetite for risk.

"It's mostly in deposit accounts that we saw the most pronounced differences," Haji said. With their propensity for saving, she added, "there's a big opportunity for educating this generation to help them grow their assets."

(Read More: How Much Financial Advice Do We Need?)

Assuming those assets survive an economic comeback, that is. The Great Depression made a permanent imprint on how the Greatest Generation related to money, but a rapidly urbanizing America—not to mention a World War—forced many of that cohort to be independent even as they scrimped and saved.

There's no telling what today's youth will do once they leave the childhood homes—if they ever do.