A 20 year old who is a full time student would be a dependent under the Qualifying Child rules. Under those rules their income is not relevant, only if they provided over one-have of their own support would they not be able to be claimed as a dependent.
To be a Qualifying Child -
1. The child must be your son, daughter, stepchild, foster child, brother, sister, half brother, half sister, stepbrother, stepsister, or a descendant of any of them.
2. The child must be (a) under age 19 at the end of the year, (b) under age 24 at the end of the year and a full-time student or (c) any age and permanently and totally disabled.
3. The child must have lived with you for more than half of the year. Temporary absences while away at college are considered living with you.
4. The child must not have provided more than half of his or her own support for the year.
5. If the child meets the rules to be a qualifying child of more than one person, you must be the person entitled to claim the child as a qualifying child.
6. The child must be a U.S. citizen or U.S., Canada or Mexico resident for some portion of the year.
7. The child must be younger than you unless disabled.
Go back to My Info on the left side of the online program screen. Edit the dependent and carefully check your answers to the questions.
Make sure you select them as your Child, that you selected that they lived in your home for the Whole Year, temporary absence for education is deemed living in your home. That they did NOT provide over one-half of their own support (You Did), that you indicated there was no one else in the household providing support to them, and that you did NOT check the box labeled Not valid for employment in the Social Security number section.
If all your answers are correct then delete them as a dependent and re-enter.
