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:) Not bad, actually. I doubt that I could have done as well when I was 11. Pixel art is usually smaller, and drawn dot-by-dot rather than using the tools provided in MS Paint and such, but you seem to have a pretty good understanding of shading and so on, so I wouldn't be surprised if you have a developing talent here.
I agree with Wulvaine 100%. Its not pixel art unless each pixel is placed by hand. It's much easier to get better if you start with smaller pieces too.