Here are the detailed requirements for claiming an 18 year old as a qualifying child dependent:
1. The child must be your son, daughter, stepchild, foster chld, 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 (or your spouse, if filing jointly) unless disabled.
He is not required to file a tax return if the earnings are reported on a W-2. If federal income tax was withheld, he should file a tax return to get a refund.
If the earnings are reported on a 1099-MISC or on no forms, he must file a tax return to pay 15% self employment tax. If he files a tax return and can be claimed by you, he must indicate on his tax return that he can be claimed by someone else.
