Family green card applications to the United States are roughly divided into five categories, starting with immediate relatives such as spouses of United States citizens, children (unmarried 21 and under of United States citizens), and parents of United States citizens. Applications in this immediate relative category are processed the fastest and generally within one year.
Other categories includes:
First preference: Unmarried, adult sons and daughters of U.S. citizens (adult means 21 or older.)
Second Preference (2A): spouses of green card holders, unmarried children of permanent residents
Second Preference (2B): Unmarried adult sons and daughters of permanent residents
Third Preference: Married sons and daughters (any age) of U.S. citizens
Fourth Preference: Brothers and sisters of adult U.S. citizens.
Although each of these other categories are possible to facilitate sponsorship for green cards to the United States, the processing time is longer in each successive category and can take several years in some instances.