Credit cards for a teenager? Some financial experts say its a good idea to give them one. The New York Times did an extensive article where some financiers feel that teenagers with credit cards can learn important lessons about money. With a proper limit set, a credit card could teach teens financial literacy within a “controlled environment.” 17 percent of adults in a survey said their children between the ages of 8 to 17 already have a credit card. Here’s what to remember. As a parent, you’ll have to co-sign on the card if they are under 18-years-old and you are financially on the hook for what they don’t pay.