FB-1 Unmarried Sons and daughters over the age of 21

A U.S. citizen may petition for their unmarried sons or daughters over the age of 21, and their children, if any.

If  the unmarried son or daughter of a U.S. citizen gets married prior to becoming a permanent resident, then he/she no longer qualifies under this category and will convert to the category of Married Son or Daughter of a U.S. Citizen. This change in categories may result in a significant delay in the immigrant visa becoming available.