Why my 16 yo son, which is an US permanent resident with an ITIN # is automatically listed on the "Credit for other dependents" box and not on the child tax credit box?

Unfortunately, you may not claim the child tax credit for a child with an ITIN. The child must have an SSN to be a qualifying child eligible for the child tax credit (CTC) or the additional child tax credit (ACTC).

Thanks for the quick answer. So if my son applys and gets a SSN, he could be eligible for CTC?

Yes, if he receives a Social Security number he would qualify for Child Tax Credit.

Once he turns 17, as long as you can claim him as a dependent the credit reduces to $500.

Rules for Claiming a Dependent on Your Tax Return