The length of your credit history counts for 15 percent of your score, which puts younger consumers at a disadvantage. Unfortunately, you can’t make yourself any older. There is one option, says John Ulzheimer, president of consumer education at SmartCredit. “If you can get a parent to add you as an authorized user on an older card, you’re going to get an immediate boost to your score,” he suggests. “It’s free, it’s easy and you have no liability for the account.” If the primary user misses payments, though, take yourself off the card; any benefit you get from the older account will be canceled out by the negative payment information. Meanwhile, keep your oldest card active as long as you don’t have to pay an annual fee.