How a teen can start out and stay credit card free. There are are a few ways to build credit besides credit cards.
Take out a loan, put the loan money in a savings account as collateral, pay on the loan monthly. A younger person may need a co signer, a parent or another adult may have to do the co signing or post collateral. This does not have to be a huge loan, $500 should be enough and try to take it out for at least a six month time frame to get a good history established. From there a younger person has a really good start on credit and can continue to borrow, probably with out a co signer on the second loan depending on the age of the youth.
This is a much better approach than applying for high intrest credit cards that if you fall behind on, they will ruin you for the next seven years, or until you give into an unforgiving collection agency who hounds you to pay. If you fall behind on these cards there are also outrageous fees, both late and the over the limit fees.