My first card was at age 18, when I joined college. When you are in college, lots of compaines give you (as a student) card very easily.
I have 3 credit cards, two from visa, one from amex. My bills are paid on time always. I try not to charge more than I can pay back. That is a good rule to keep. There is no use buying something you cant afford. Keeping that rule I always pay it in full. Only once have I had to break teh payments up into two (but that was because somethign came up and I didnt have enough to pay it in full).
Credit cards are good to put things off, but when shopping for credit cards makes sure that its got "no annual fee, if there is one not more than 40 bucks", "25 day grace period". The APR doesnt bother me because I dont keep balences.
anyway check this link out:
Teen Advice Online . Org - Establishing Credit
Edit:
Be smart in balencing your payments, I keep track of my accounts (bank/credit cards) regularly, so I know where to spend money from (which account) even though it may look like I am not in a good position. Right now I am going thru my bank account I have give my credit cards a rest for 2 months (0 balence), the only one I got to pay is a 1400 dollar bill (on my amex) for my airline tickets that I would pay tommorow. After which I am pretty much clean, so on my vacation I dont have to be hasseled with bill payments knowing its all payed and I can spend like mad rat.. ofcourse when I get back it will be back to the same cycle.. pay pay pay.