In the first page, this is written:
六{むっ}つのとき、原始林{げんしりん}のことを書{か}いた「ほんとうにあった話{はなし}」という、本{ほん}の中{なか}で、すばらしい絵{え}を見{み}たことがあります。
I don't have the English version, but the Brazilian version says the equivalent of:
Once upon a time, when I was 6 years old, I saw in a book about the Virgin Forest, Real Stories, a impressive drawing.
Would it be correct if I said something like 私が六歳のとき?