I love that you kept them like the original in color and pieces. I do think that it is a bit too pyramidal. Also, again, MORE GUNZ!!! Would you go to battle, with a bunch of emotionless robots shooting you, with nothing but a little turret?! NO! You go with machine gunz, and rockets everywhere! Sorry, my little tangent. Anyways, something to think about.
As a 21-year old, I consider this good. The shape is a bit basic (a result from it consisting of mainly big pieces and standard techniques) and the colour scheme a bit boring, but you're on the right track (to what I consider good lego building - mileage may vary). Keep it up, and don't forget to experiment with smaller and more interesting pieces.
Who cares if you're 12? This is much better than the average 15 year old on MOCpages, easily. No halo, bionicle, or stickers involved. I'm 17 by the way. I like the whole look of it...sleek, low and powerful. I'm not sure about the back thouhg...the 1x4x3 panels seem plain and lacking, and angular compared to the rest. Perhaps some detailing would be in order there? Keep at it!