Even if you could claim the child----which is questionable -- since he is not related to you, all you would "get" would be the non-refundable $500 credit for other dependents. Since he is not related to you, you cannot get the child tax credit, earned income or head of household filing status for claiming him. (and...if he was 17 before the tax year ended, no one gets child tax credit for him. Only a child 16 or younger qualifies the parent for child tax credit).
IRS interview to help determine who can be claimed:
https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent
https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
