The age requirement for derivative children is that they be under age 21 at the time the I-526 Petition is filed. A derivative child may still age out if a visa is not immediately available after I-526 approval (which currently only affects Mainland-born Chinese nationals). Once a derivative child receives a conditional Green Card, however, age is no longer a factor—the conditions on his/her Green Card will be removed when the I-829 Petition is approved.