20 CFR §10.405

1. (a)Dependents include a wife or husband; an unmarried child under 18 years of age; an unmarried child over 18 who is incapable of self-support; a student, until he or she reaches 23 years of age or completes four years of school beyond the high school level; or a wholly dependent parent.
2. (b)Augmented compensation payable for an unmarried child, which would otherwise terminate when the child reached the age of 18, may be continued while the child is a student as defined in 5 U.S.C. 8101(17).