The unmarried son or daughter of a U.S. citizen who is over the age of 21 does not qualify for the immediate relative category. However, the child will qualify under the family first preference (F1) category. If the petitioner wishes to petition for more than one adult son or daughter, separate petitions must be submitted for each son or daughter.
To qualify for this category, the adult son or daughter must have met the legal definition of “child” when he/she was younger than 21 under U.S. immigration law. The beneficiary must have an approved immigrant petition (I-130) and wait for a visa number to become available before applying to adjust status in the U.S. or to obtain an immigrant visa abroad at a U.S. Consulate.
If the child gets married while waiting for a visa number to become available, he/she will drop to the Family Third Preference visa category, where the wait time tends to be even longer.