1.That boy is too young to go to school
那个男孩太小以至于不能去上学（too...to..）
2.That boy is so young that he can't go to school
那个男孩太小以至于不能去上学（so...that...）
解析：
young [jʌŋ] adj.年轻的；初期的；没有经验的
n.年轻人；（动物的）崽,仔
[ 比较级younger 最高级youngest ]
so...that...：太...以至于；太...而(肯定和否定都可)
too ...to...：太.而不能