it’s about his life when he was ten years old

[diamondcutter]

The film’s from a book by Gerald Durrell and it’s about his life when he was ten years old.

(Kid’s Box 6, Caroline Nixon, CUP)

I wonder how to paraphrase the relative adverb “when”. What about this: during the period of his life?

 

[diamondcutter]

Thanks, Picean.

Since the “when” = “a preposition+which”, I want to know what the “which” refers to.