Going back to the U.S as a resident after 3 years overseas.?

Alright so heres the deal..I was born in Argentina but my family moved to the U.S when I was a kid. I became a resident there and what not..3 years ago we moved back to Argentina. Now my 18th birthday is coming up in a couple of months, I wanna move back to the U.S get a job there and an apartment with a friend. Now, My main concern is, Since I'm already a permenant resident can I just buy an airline ticket and go back with no trouble? Will I be allowed back in the country? I know for a fact my resident card hasn't expired cause I have it with me. So if anyone can tell me what I'm gonna need to get back in the country and anything I need to know then I'd really appreciate that. Thanks in advance.

By the way, My sister was born in the U.S so she's an American Citizen by default..I don't know if this helps but I thought I might add that lol.

Three of the answers you have received so far are correct. You have been gone from the U.S. far too long to be considered a permanent resident. If you attempt to return to the U.S. as a returning resident after a three year absence, you can be detained for a hearing before an immigration judge.

There was a precedent decision made many years ago for cases like yours. In that decision, the Board of Immigration Appeals ruled that when the parents of a child abandon their resident status, the abandonment also applies to the children who are under their control. As you were under the care and control of your parents 3 years ago, you are considered to be an abandonment too.

A child cannot form the intent necessary to establish his
or her own domicile. A decision to abandon permanent resident status by a parent applies to a child under his control.

I'd say that if you can't find the information you need at the site I've linked to below, you need to contact them and ask. Sorry, I can't help any more than that.

If I understand right, you have a "Green Card" and unlike your sister, you are not a citizen. If I am right, you can only stay for up to an year or so and then enter the US without any restrictions even though your Green Card has a validity of 10 years (or more). If your stay is over an year you will have to obtain a re-entry permit from US immigration. Please check their portal site: http://www.uscis.gov/ for information or contact your local American Embassy for clarifications. Your sister requires no such permit.

Under certain conditions, permanent residence status can be lost. This includes committing a criminal act that makes a person removable from the United States. A person might also be found to have abandoned their status if he or she moves to another country to live there permanently, stays outside the USA for more than 365 days (without getting a re-entry permit before leaving), or does not file an income tax return. Permanent resident status can also be lost if it is found that the application or grounds for obtaining permanent residence was fraudulent. The failure to renew the permanent resident card does not result in the loss of status, except in the case of conditional permanent residents as noted above.

It sounds like you have abandoned your permanent resident status, UNLESS you have a re-entry permit.

I'm sorry to tell you this, but you are no longer a permanent resident. You are considered to have abandoned your US residence status after being out of the country for 1 year. There is no way to recover it after 3 years.