There is no fixed rule. School start with class 1, ie 6-7 years. However, some children can read, spell, since 5 years. I was such a child. But this desire because of my mother who sat next to me and teaches me baby although I did not have such fancy things.
If mother, grandmother, sister, brother, father, or anyone else sitting next to a child teaches the child will learn whether it's five years or 12. Left on their own, children can not learn, because learning seems interesting.
We live in the world of Internet and television, but without knowing even trivial thing to read, nothing all the technology.