HE WILL BE 19 BEFORE DEC 31 AND WORKS FULLTIME
The easiest way to figure this out is by going to a CPA or qualified tax preparer. There is a specific test for what makes a qualifying dependent. The only probably part of the test you won't meet is probably the support test if you did not provide more than 1/2 the child's support for the year.
IRS Publication 501
This is not legal advice nor intended to create an attorney-client relationship. The information provided here is informational in nature only. This attorney may not be licensed in the jurisdiction which you have a question about so the answer could be only general in nature. Visit Steve Zelinger's website: http://www.stevenzelinger.com/
Are you a U.S. citizen? What is your marital status? Did you provide more than half of his support? Do you intend to file a joint return with your spouse? These are the questions you must answer to determine whether or not you can claim your son as a dependent. Go to the following web site and the IRS will walk you through the analysis:
Generally he will meet the age requirement for this last year. However, as they point out, there are other requirements. If he goes to college, you can claim him until the age of 24, under the age part of the test. The residence requirement will be met even if he goes away to school as long as he isn't making his own money by working. But this can also change if your ability to claim him was granted by divorce decree.