OP - This web site will provide answers to your questions at www.irs.gov/publications/p17/ch03.html.

It would seem that for 2015 Taxes since your son was under age 19, you will be able to claim him as a Child Dependent. Then for 2016 and subsequent years you will need to follow the rules of a Qualifying Relative which depends on whether the individual also is filing an income tax and the amount of direct support which you provide.

It must be frustrating to have DS just sort of "drifting." Since he can be on your health insurance, I would try to connect him up with a therapist who might help him sort out hs issues and get him to see the importance of taking his medication for ADHD just to be able to get on with his life and do something. It is reasonable to set some expectations for living in your home and on your direct support to either be pursuing the GED or looking for at least a part-time job. He also should be expected to be an independent young adult in your household - doing his own laundry, caring for his room and bathroom, preparing at least some of his own meals and doing tasks such as yard work, cleaning main areas of home,too, if he is just sitting around.

If your DS is in Virginia and has the documented disability, he may also qualify for job support services through the Department of Aging and Rehabilitative Services (DARS) The assessment is free and perhaps it would give him a sense of direction if he could see what areas of strength he has etc.

OP - for your information, you can actually keep DS on your health insurance until he is 29 if you use COBRA. Just something to know if should still be in need of health care coverage for any medical condition. If he made if almost through high school, maybe it is time to find out about the GEd program in your area.

I have no tax knowledge beyond filling out our own returns, but while I think your DS does not meet the criteria as a qualifying child since he is 19 but not a full-time student, he DOES still meet the criteria for a qualifying relative and you can claim him as a dependent. He's living with you and you're covering more than 50% of his expenses.

If your DS is living with you or in school with your home as a primary residence, and you are paying his expenses, he is still a dependent. We claimed our 19 year old (living at home) and our 21 year old Ifull time student). Taxes done by a good accountant, so I assume it was legit.

Also, OP, this has nothing to do with your original question, but I thought your DS might be interested. The Smithsonian offers a free coding class over the summer called All Access Digital Arts Camp:
http://www.si.edu/Accessibility/access-camp

The application is from 2013, but there's contact info in case you'd like to get an updated one.

OP,

I don't know the answer to your question. Just as an FYI though the Ivymount Resource Fair is today at noon. It's free and open to the public. This group is one of the exhibitors:

"The Meltzer Group, Michael Orleans • www.meltzer.com
Planning for the future needs for a loved one with a disability can be daunting. I have the knowledge, resources and passion to assist individuals and families to navigate and manage the complexities of future care, government benefits, and financial needs that come with planning for a child with special needs. Exhibit Table: GYM 27"

I don't have any experience with them, but they sound like they'd be able to answer your question. This is the link about the fair/directions: http://www.ivymount.org/programs.cfm?subpage=1828

I am not sure if I clam my son as a Dependent. He turn 19 on April 4, 2015. He only attnd NOVA from Fall 2014. He failed and didn't not go back. He has ADHD but he is not getting any kind of assistance from the government. From what I understand he can't be a dependent is that true?