Welcome to FT jys55! Probably not the right forum for this question so be aware the mods may decide to move it soon.

To answer your question, you can always start building a good credit history. Given your age and possible lack of credit history, you may find that you will not be approved for some of these credit cards. No one here can accurately predict your chances of success; there's just too much information credit card companies use to assess you as a credit risk and an analytical engine that sometimes produces uneven results when presented with similar facts.

If you decide you're going to start taking credit cards and you're getting offers in the mail, take a look at this thread in the MilesBuzz forum, http://www.flyertalk.com/forum/miles...-up-bonus.html, before you apply for any of those deals. The letters you're receiving are probably offering 30-40K for signing up. Read post #2 in that thread carefully, and you'll see that for the same credit inquiries, you'll qualify for at least 75,000 AA miles instead.

That post sets forth a method for qualifying for 225,000 miles in roughly three months, but the chances of success in getting all three cards required increase with a longer and stronger credit history. And, given that you're just getting started with credit cards, you'd probably be better off dipping your toe into the waters with one card, keeping in mind that no credit card is worth the bonus if you have to start paying interest charges. The general advice here is to pay your monthly balance off, in full, every month. That helps you avoid interest charges that can take a chunk out of your budget fairly quickly while helping you to build a good credit history--that will later allow you to take more cards if you wish.