It's complicated. There are two types of dependents,
"Qualifying Children"(QC) and standard ("Qualifying
Relative" in IRS parlance even though they don't have to actually be
related). There is no income limit for a QC but there is an age limit, a
relationship test and residence test. Only a QC qualifies a taxpayer for the
Earned Income Credit and the Child Tax Credit. They are interrelated but the
rules are different for each.
A child of a taxpayer can still be a qualifying child dependent, regardless of his/her income, if:
1. He is under age 19, or under 24
if a full time student for at least 5 months of the year, or is totally &
permanently disabled
2. He did not provide more than 1/2 his own support. Scholarships are
considered third party support and not as support provided by the student.
3. He lived with the parent
(including temporary absences such as away at school) for more than half
the year
Because your 19 year old is not a full time student, he can not be a Qualifying Child. So, now there is an income test for him to be a dependent. He can only be your dependent if he has less than $4050 of income.
A person can still be a standard dependent (Qualifying Relative) if not a Qualifying Child, if he meets the 6 tests for claiming a
dependent:
1. Closely Related OR live
with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4,050 (2016-17)
3. The taxpayer must have
provided more than 1/2 his support
In either case:
4. He must be a US citizen or resident of the US, Canada
or Mexico
5. He must not file a joint
return with his spouse or be claiming a dependent of his own
6. He must not be the
qualifying child of another taxpayer
