To claim your child as your dependent, your child must meet the qualifying child test or the qualifying relative test.
To meet the qualifying child test, your child must be younger than you and as of the end of the calendar year, either be younger than 19 years old or be a student and younger than 24 years old, or any age if permanently and totally disabled.
There is no age limit on claiming your child as a dependent if the child meets the qualifying relative test.
In addition to meeting the qualifying child or qualifying relative test, you may claim a dependency exemption for your child as long as all of the following tests are met:
Dependent taxpayer test
Citizen or resident test, and
Joint return test