My older children were independent readers at a huge variety of ages. One was reading novels at three years of age. Others learned to read around five, and progressed at a similar rate to most schooled children. A couple of them could read basic words, but weren’t independent readers until they were 8 or 9 years old. I define an “independent reader” as one who will seek some text to read for pleasure, or obtain information, without much assistance. Most of our kids jumped from “The Cat Sat On The Mat” style readers to novels or non-fiction books in a matter of weeks.
As adults, they all read for pleasure and study. They’ll often come home and scour the bookshelves for favourites to re-visit or reference books they remember.