If he was age 19 in 2016 and not a full time student, then you could only claim him as a dependent under the Qualifying Relative rules. Under the rule the dependent must not have gross income of $4,050 or more. If his gross income for 2016 was $4,050 or more then you will not be able to claim him as a dependent on your 2016 tax return.
To be a Qualifying Relative -
1. The person cannot be your qualifying child or the qualifying child of any other taxpayer. A child is not the qualifying child of any other taxpayer if the child's parent (or any other person for whom the child is defined as a qualifying child) is not required to file an income tax return or files an income tax return only to get a refund on income tax withheld.
2. The person either (a) must be related to you or (b) must live with you all year as a member of your household.
3. The person's gross income for the year must be less than $4,050 (social security does not count) in 2016
4. You must provide more than half of the person's total support for the year.
5. The person must be a U.S. citizen or a U.S., Canada, or Mexico resident for some part of the year.
6. The person must not file a joint return with their spouse.
