In a sobering study by Rent.com, more than three-quarters of renters from the ages of 18 to 24 overspend their monthly incomes by $100 each and every month. The culprit is high living expenses; 42 percent say rent is their top expense, while 22 percent say it is food, and 18 percent say it is transportation. What is more, these young adults are largely using credit cards to make up the difference, creating a long-term debt that they will likely never finish paying off. This will create a financial drag on them well before they reach their peak spending years. Retirement? What retirement?