英语翻译The boy（）these difficult problems by himself

填hasn't reach the age to deal with 或者is not old enough to deal with
第一句中hasn't reach the age 就是“没有到达XXX年龄的意思”,算是直译.
第二句中稍稍变通了一下,“还没有到独立处理这些难题的年龄”可以转换一下思维,变成“不够年长,所以处理不了”,not old enough 就是“不够老”的意思
以上两者均可