Understanding トムは高校生のころ拒食症になった。


The sentence

> トムは高校生のころ拒食症になった。

apparently translates to

> Tom became anorexic when he was a high school student.

My confusion is how the phrases

> 高校生のころ

and

> 拒食症

grammatically fit into the sentence.

  1. Is に marking the entire phrase 高校生のころ拒食症, so that the sentence parsing is something like this:

> トムは((高校生のころ)(拒食症))になった?

  2. Is 高校生のころ an adjectival phrase modifying 拒食症? If not, what is 高校生のころ classified as? And why doesn't it have its own particle marking it?




In this sentence ころ is used as "when", so the parsing is トムは(高校生のころ)(拒食症になった)?

Smth like "Tome became anorexic when a high school student"

So, it's a separate clause if you like.

Can't resist putting unrelated quote from Three in a boat "... and wish I'd
been kinder to my little sister when a boy"

Also see here [What does の頃【ころ】 mean in this
sentence?](https://japanese.stackexchange.com/questions/15308/what-
does-%e3%81%ae%e9%a0%83-%e3%81%93%e3%82%8d-mean-in-this-sentence) , it seems
it' especially common usage with high school for some reason

