I remember I was awful at reading books at my primary school (didn't read them much) because I found them too easy and therefore boring (was more interested in Horrible Histories).
However, I don't really remember when I was able to read fluently, or when I started finding school books way too easy for me. The earliest I was reading Horrible Histories that I remember was when I was 8, and I completely understood the books. Horrible Histories had books with around 100 pages, I think.
Yeah, biggest book I have of that series is ~250 pages and that's a combination of two of the books. So yeah, around 100 pages in a single book in the series.
I kinda miss reading that series. Might read again.
SQ