American Children, Teenagers and Young Adults: Of the 4,000 students who took the Jump$tart personal finance survey in 2004, 65.5% received failing scores. A study of 1,065 teens found that 21% of 18 and 19-year-olds have credit cards. People in the 18 to 24 age bracket spend nearly 30% of their monthly income just on debt repayment – double the percentage spent in 1992 (10% of net income is a recommended amount for debt obligation).