Apologies if this doens't come out right, I'm a little drunk right now, but I have nothing else to do...
1) Servers can be variable in cost. You could host it yourself, but the charges for the badnwitdth would come through your ISP. To actually rent a server it'd anywhere from 100 - 400/month... I think.
2) No age is really specified, you can learn it whenevr. The only barrier to your game programming would be the math, which you don't learn when you're 13. When I was 13, I was just getting used to algebra and stuff, I hadn't started functions, trigonometry or antyhing like that.