老师说enough to do sth.=be so+adj.+(that)肯定句,又说not enough to do

The girl was old enough to go to school. The girl was so old that she can go to school.
The girl was not old enough to go to school.The girl was so young that she can't go to school.The girl was too young to go to school.
英语中一个意思可以用多种句式来表达,仔细体会,这几个句子,无非就是想表达那两个意思.