No, you cannot claim the Child Tax Credit for your child who is 18 and still in high school. The Child Tax Credit is only available for qualifying children who are under the age of 17 at the end of the tax year
However, your 18-year-old child may still qualify as a dependent and for other credits, such as the Earned Income Credit (EIC) if they meet certain criteria
For more detailed information, you can visit the TurboTax Child Tax Credit Guide
and the IRS Child Tax Credit page
