To apply for your parents’ green card, you need to be at least 21 years old and a US citizen. Start by filing a Petition for Alien Relative (Form I-130) with the U.S. Citizenship and Immigration Services (USCIS), followed by an Affidavit of Support and an application for Green Card (I-485) or consular processing if they’re overseas. Each step comprises various procedures, submission timelines, and fees.