Depends on what you mean. They learn skills to do higher math and reading from about age 2-3 and keep building. It's not a cut and dry thing. It's an ongoing thing to build the foundation.
My 5 year old is in Kindergarten and doing it now.
Whenever you start working on them with your LO. My youngest has been doing that since about 3 1/2...very basic but a good start
Sorry everyone, updated the OP :)
In schools here they start reading and math in kindergarten. So 5 for basic sight words or whatever. Dd is in pre k and they're teaching the alphabet. As far as recognizing letters and being able to write them.
Oh based on your example I have some 4 yr olds in my class that do that but on our assessment tool it's in the kindergarten range.
Kudos to you! It just shows that you or someone is working with him. My daughter has been pretty good about counting and adding for about a year. I didn't even realize she was good at it until my cousin (who was doing lab work for school with her) had her count and sort m&ms.