Considering that your drawing was done in MS Paint with a mouse, that's not that bad.
While I could say something like "you can do anything that you put your mind to", or some similar appeasing generalization, the truth is that you really have to put almost all your time into becoming a game artist. I spend probably 80-90% of my free time working/reading game art, and I still have a long way to go. Unfortunately, even if you work very hard for a long time, things might still not be working out, or going the way you wanted to. Not everyone who "puts their mind to it" can get a PhD. in physics, for example. Sure, maybe they can after 50 years, but what good is that?
But the key here is if you know that this is something that you really enjoy (do some research first), and you devote yourself to an ideal (game art, games, etc), then I am sure that it will work. If not, well at least you have a cool hobby
