一、of the same age：一般作be 的表语或在名词后定语。蒋老师的例句都是作定语的，网友的句子是作表语的。我再举一些作表语的例句：

The sandstone and shale units are of the same age. 砂岩和页岩单元是同时的。

All of the boys in the class are of the same age. 这个班上的男生年龄都一样。

My wife and I are of the same age. 我和妻子同年。

【注】be of + 名词（抽象意义），在很多情况下表示“拥有”之意，可以理解翻译为have，例如：

Basic research is of great importance in all scientific fields.  

在各个科学领域里,基础研究很有价值。

We were both of the same nationality. 

我们俩有同样的国籍。

He and I are of the same height. 

他跟我有同样的高度。

二、at the age of：不能用于表语，只能作状语，修饰谓语动词。

He ran away from home at the age of thirteen.

他十三岁那年就离家出走了。

At the age of thirty, Mary began to lose colour.

玛丽在30岁的年纪就红颜渐逝了。

She was orphaned at the age of ten.

她在十岁时成为孤儿。

My father retired at the age of 60.

我父亲六十岁时退休了。

My grandmother got married at the age of seventeen.

我的祖母十七岁就结婚了。

He was already balding at the age of 25.

他25岁就秃顶了。