同意童老师关于定语从句的分析。提问者可能对something本身的作用也有疑问，补充如下：

这个句子的结构是：分句，+ 名词/代词+后置修饰语。可以理解为名词前省略了which is。这个句子可以改写为：

Akhtar is currently taking seven AP classes, which is something he says that not many students his age are doing. which引导非限制性定语从句，先行项是整个谓部，即is taking seven AP classes. 或者：

Akhtar is currently taking seven AP classes, and this is something he says that not many students his age are doing.

which引导非限制定语从句，其先行项不仅可以是主句的一个名词，也可以是主句中的一个形容词、动词或整个主句的内容。如：

Tom is tall, which I am not. (which的先行项是tall)

Tom dances well, which I can't. (which的先行项是dances well)

Tom dances well, which is true. (which的先行项是整个主句）

这句话中，which is省略后，something+定语从句是一个名词短语，对前面句子做补充说明。叫它名词作状语？右偏置结构？同位语？省略了成分的非限制性定语从句？喜欢哪个就叫那个吧。反正搞语法的也在争论呢。