You can claim a child as a dependent on your tax return as long as they meet the IRS criteria for a "qualifying child" or "qualifying relative." The key age limits and conditions are:

• Under age 19 at the end of the tax year, if they are not a student.
• Under age 24 at the end of the tax year if they are a full-time student for at least five months during the year.
• There is no age limit if the child is permanently and totally disabled.
• The child must be younger than you (or your spouse if filing jointly).
• You must provide more than half of the child's financial support.
• The child must live with you for more than half the year, with some exceptions for temporary absences like education or medical care

If the child no longer meets these age or student criteria, you might still claim them as a qualifying relative if they meet other dependency tests, including income limits and support tests. For divorced or separated parents, generally only one parent can claim the child as a dependent, usually the custodial parent unless the custodial parent releases the claim via IRS Form 8332

. In summary, you can claim a child as a dependent until they turn 19, or 24 if a full-time student, or indefinitely if permanently disabled, provided other IRS dependency tests are met.