You are pretty good. But, if you want to get a job, first you must choose three or four of your best. Try to show knowledge of human anatomy, animal/creature and machinery. Only if you want, do some building/escenery, but, that sort of things usually are done by other people (specialized if you want).

Also, your drawings should show movement (like a guy kicking another, jumps, crouching animals, etc)... because it's harder to do than "static" images.

Then send your sample work to game studios, and, if they are interested, send the rest. If they critizes you, listen, improve and try again.

Usualy, they will do that only to make sure you are really commited and interested in getting a job.

The art itself is pretty good. A couple things, some of which have been mentioned:
-Dynamic poses, they demonstrate the persona of the character as well as make the drawing interesting.
-The second drawing looks strange, the third drawing is a wierd pose. The first is my favorite, even with the distorted anatomy
-Most importantly, though, are your designs. More important than artistic talent is creative talent. You need to be able to conceptualize in detail a range of characters... a handful of concept artists can do all the art for a game, the position is very coveted. The designs are very basic, right now. Do some elaborate designs, and do some more gestural/dynamic designs. The portrait isn't so important, its whats going on in the portrait that's important.

Overall, though, amazing considering your age. Definately keep practicing, increase your range of styles, and keep studying life and figures. I couldn't draw that well when I was that young, and you definately have a good understanding of anatomy (second drawing especially, its muscles are correct though its proportions are wrong, usually its the other way around if anything is correct at all). I'd definately try to get onboard with some promising volunteer games and mods, try to do a new one every couple months in different styles. Traditional art skills are in high demand on the mod scene, you'll be able to help alot while getting good experience. I'd try to look for paid work once high-school is finished, it'd be difficult before that (unless its a very small paying indie project). Great work though.

thx for the comments and advice guys!