Two-thirds of Millennials, who are 18 to 34, save the cash left over from their paychecks and 18% of them pay off debt, according to a study by market research firm Lab42, out Tuesday. Most of their debt is credit card and student loans. How will they manage debt as they take on mortgages and other major loans, asks Gauri Sharma, CEO of Lab42. It's also unclear how well they will invest for their future. Now 43% of them describe themselves as conservative investors, according to a study released in February by management consulting firm Accenture.