That's how congress wrote the law.
Your child is too old (over 16).You can still claim your child, as a dependent. What you can't claim is the
Child tax credit. This comes as a big surprise to many parents the year
their child turns 17. A
child over age 16 no longer qualifies for the Child Tax credit (CTC). Although a child can
still be a student dependent through age 23, and a qualifying child for
EIC, the Child Tax Credit expires the
year they turn 17 and you no longer get the $1000 CTC.