@marvsains64
The key thing you need to focus on is "unable to perform substantial gainful activity" (where "gainful" means earning money). Working at a sheltered workshop for persons with disabilities is not considered gainful activity even if he is paid, but being able to hold down a minimum wage, part-time job would be considered gainful activity. If audited, you may need to prove the disability with a letter from a doctor or other qualified professional.
Also, the only tax benefits of claiming a dependent over age 16 (regardless of if they are considered a qualifying child or qualifying relative dependent) are:
1. a $500 credit for other dependent
2. eligible to claim the child and dependent care credit if you have to pay for someone to watch your child while you are at work because they can't take care of themselves without supervision
3. can claim medical expenses you pay for your dependent as itemized deductions
4. can carry your dependent on your health insurance past the age of 26 (but verify this with your insurance carrier).
