I seriously wouldn't know. I've been reading as long as I can remember. My older brother is 20 months older than I am, and I have always read what he was reading. My parents also were readers, so books were always available. My younger brother, however, didn't read (unless he had to), so having books available doesn't always mean you start reading.
I was so glad when my older brother was finally deemed old enough to go to the big library in town (instead of that smaller we had in our village), and I was allowed to go with him (it was about 10km by bike). I was 11 then and had read about every book in our local library...