Child tax

No, you do not have to be a certain age to claim a child on your taxes.  However, you do have to meet certain qualifications.  

To claim your child as your dependent, your child must meet either the qualifying child test or the qualifying relative test:

• To meet the qualifying child test, your child must be younger than you and either younger than 19 years old or be a "student" younger than 24 years old as of the end of the calendar year.
• There's no age limit if your child is "permanently and totally disabled" or meets the qualifying relative test.

Also:

• They're related to you.
• They aren't claimed as a dependent by someone else.
• They're a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They lived with you for more than half the year (exceptions apply).
• They didn't provide more than half of their own support for the year.