网友对我这个解答：http://ask.yygrammar.com/q-36731.html  存在疑惑。

我在提交上述解答后，发现提问的网友已经刚采纳了另外一个解答。

现在，我把这个解答贴在这里，让各位老师和网友讨论吧。我自己就不作说明了。

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▲ “一个15岁的学生”，记住这些正确的表达，错误的自然就知道了。

a student of fifteen

a student of fifteen years old

a student of fifteen years of age

a student fifteen years old

a student fifteen years of age

a student age fifteen

a student aged fifteen

a fifteen-year-old student

（说明：以上表达，fifteen 可以换成阿拉伯数字 15 ） 

▲ 我时常见到下面这些貌似正确、实则错误的表达：

a student at fifteen

a student at age fifteen

a student at the age of fifteen

The student is at fifteen.

The student is at age fifteen.

The student is at the age of fifteen.

▲ 这些词组本身不错，但不能作定语或表语。它们作时间状语。

(at fifteen； at age fifteen； at the age of fifteen)

The student left school at fifteen.

The student left school at age fifteen.

The student left school at the age of fifteen.