God is just. He will punish wicked people according to the quantity and quality of their wickedness.
Says who?
Also, you are phrasing that incorrectly... "God is just" implies that justice exists without God... It's like saying, "God is good"... well... that's not what you believe... you believe, "Good is God"... whatever God does is just/good, not because the act itself is good, but because anything God does is exempt... If God decides to murder innocent Egyptian children and animals by the tens of thousands, its just/good because God did the murdering of innocent children (see the 10th plague of Egypt)
You believe that whatever God does is just/good, not because murder is just/good, but because when God does it, he's special and exempt...
Now imagine as an example that you were 20 years old, and had been wicked all your life. By the time you were, say, 50, wouldn't you have done a whole lot more wickedness? If you die at 50, you have a lot more to be punished for in Hell than you would have if you died at 20.
Why do you assume that someone who doesn't believe in God is wicked/evil? Are all atheists wicked in your eyes? What about Muslims, Hindu, Buddhist? All evil too?
Just because someone doesn't believe in Santa without evidence, does not make them evil... it makes them less gullible than you...