Your return was not rejected because of a dependent over 17. It must have been rejected for some other reason. it is true that if your child turned 17 before 2018 ended, you cannot get the child tax credit. You can, however, claim the child as a dependent and get the $500 credit for other dependents.
What is the rejection code or message you received?
**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.**