The age to stop paying child support varies by state, but in some states child support ends when the child turns 18 and graduates from high school. The age of majority is the legal age established by the laws of the state that declare an individual an adult.
While most state laws use 18 as the age when child support ends, some states extend it to 21. Mississippi, New York and the District of Columbia have child support laws that end support when the child turns 21. Many states will terminate child support when the child graduates high school, which could vary in age from 18 to 20 in most situations.