First, welcome!
It is definitely okay that your child has an early interest in numbers. Rest assured that this is perfectly normal for a GT child. The sensitivity to feedback and social norms is also common among GT kids, albeit a more disconcerting trait. Supporting this interest wholeheartedly and putting your child in situations where it's good to like numbers and good to be smart can help. This may mean finding GT support groups or even just having your child spend more time with older kids. Whatever works.
As for hothousing...If you're following your child's interests, you are NOT hothousing! Hothousing is parent-driven, pushy, stage-mom or -dad "you must achieve or else I won't love you!" sorts of behavior. You're clearly not doing that. Going with your child where he takes you is just good parenting.
GT kids need to learn like they need to breathe. They HAVE to do it. It's part of who they are. Support that. Don't push, but go where they want to go with it.
For 9s, there are lots of tricks to use--write down for him 0-9, then write 9-0 in reverse order and show him that 1 x 9 = 09, 2 x 9 = 18, etc. He'll probably love that! There's a way to do this on one's fingers and knuckles, too, but I don't know it off the top of my head.
One thought: if you are ambivalent, he will pick up on that. If you think it's cool that he's into math, he will be more likely to stick with it.
You're in a good place.
