Advice regarding my 8 year old son. How can I push him academically?

We live in Los Angeles after leaving the Bay Area. My son is very gifted in math (he knew his times tables by 3.5), is passionate about geography, astronomy and now…Minecraft. I hate it but I don’t tell him that. He used to love chess but that’s taken a back seat. Any programs people could recommend to keep pushing him in math. I’d rather use a text book or do something like Russian math. Please help!