Sorry----being 16 for most of the year is not what counts. If he turned 17 even on December 31, you will not get the child tax credit for him. If he was 17 before the end of 2025, you get the non-refundable $500 credit for other dependents instead of the CTC.
https://www.irs.gov/help/ita/does-my-childdependent-qualify-for-the-child-tax-credit-or-the-credit-f...
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