答案：D

题目分析：句意：这个女孩子还没到上学的年龄。enough作副词应置于形容词（或副词）之后。例如：The boy is not old enough to go to school. (这孩子还没到上学的年龄。)="The" boy is too young to go to school.(这孩子上学还太小。)I'm old enough to handle my own affairs.（我已经长大了,可以处理我自己的事情。）故选D。