For EITC (Earned Income Tax Credit), yes, he still qualifies as long as he is a dependent. However, you do not receive the child tax credit (CTC) for any child who is 17 or older. Instead, you receive the nonrefundable $500 credit for "other dependents".
Did your younger son by any chance turn 17 in 2024? If so, that could be the primary reason you are seeing a big adjustment.