My DS1 was similar. I felt that he wasn't short of a marble or two and would probably fly with academic stuff when it came time for school so I decided to avoid anything like that at home (at least if it was instigated by me).
He had access to CBeebies (and the website) and preschool (2 mornings) and I always answered questions. I just prefered that they were about the texture of mud; the length of a humming string; the time it takes for a bean to grow; how dirty you could get between baths etc.
I feel that in his case I was right. He's reading, albeit stumblingly, books aimed at junior aged children and has been in school since September. He is the old end of the year but was really ready for formal education rather than just coping with it so I was glad to have him at home for the extra time.
There was pressure on me to teach him some formal stuff but he more or less taught himself to write before he went to school from what he picked up himself.
I feel that you can teach a child anything you fancy so I'm not sure why there is the emphasis on the 3Rs before school age. If you feel he needs stimulating more he might enjoy botany, astonomy, a potters wheel, a musical instrument, dance, house design, inventing stories or poetry for you to write down, camping, cooking...
Do whatever makes him happy.