21 years for parents and siblings. Differs if you want to bring your spouse (best to check with an immigration attorney for specifics). There are quite a few documents that you need and the what-and-when depends on which family members you want to bring. Assuming they are outside the United States, you initially need to prove the relationship and file the petition with USCIS. I think it could benefit you greatly to meet with an attorney to discuss further.
You have to be 21 years old to bring your family. Here are the family relationships that you may bring to the US:
1. If you are a US Citizen, you can petition a spouse, child (any age, married or unmarried), brothers and sisters.
2. If you are a Lawful Permanent Resident, you can petition a spouse, child (any age, unmarried only).
The documents you'll need depends on the relationship to the family member. Typical documents that you'll need for yourself are: birth certificate, proof your status i.e. naturalization certificate, green card, last 3 years taxes, driver's license and passport style photos. The documents you'll need for your family member include: birth certificate, passport, I-94 card (if she is in the US), marriage certificate, police certificates (if abroad) and more.
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