PLEASE PLEASE PLEASE can I have some advice I am 11 and have no coding knowledge but would like to make a paintball shooter.
Normally this sort of thing requires you to know a programming language, or at least have an understanding of programming logic. I do have a few recommendations however that may help. If you have absolutely no understanding of programming logic I suggest you try playing LightBot, its a great little game that introduces players to the concepts of programming. From there you can move on to Kodu which provides a number of easily assembled logic blocks you can use to make a shooter style game.
If your interested in further learning after that there are a number of other resources available though opinions and tastes vary on which tools people recommend, such as Scratch, Game Maker, and Python, among others. If you have any further questions, feel free to ask.
Hm, it's a bit misleading but you don't actually need a verification Email or account to download GameMaker. From the main YoYoGames website, click on Get GameMaker, then click on the Free Download button on the next page. It will then take you to a page prompting you to make an account, ignore that and scroll to the very bottom of the screen, there you should see some underlined categories like "GameMaker", "Download", "Support", etc. Under the "Download" category click "GameMaker: Studio" and it should give you the download for the installer. For convience, here's a direct link to the download [link].
I don't have a great deal of experience with GameMaker compared to Python so I may not be able to offer much help, though I have found a few tutorials for making First Person Shooters that may prove useful. If on the other hand you want to try Python you can read Learn Python the Hard Way, it has a similar syntax and format to Scratch and serves as a good gateway to other lower level languages. There's also an open source Minecraft Clone written with Python and Pyglet over here.
Unlike Kodu, Scratch, or GameMaker, Python doesn't have any straightforward graphics or mouse/keyboard handling built in. In order to handle things like that you'd need to install a 3rd party library like Pyglet (there's a Beginners Guide here) or Pygame. There are also a few pre-built engines that use Python though like Panda3D, or Blender which comes with modelling and rigging tool's for making 3D models, although the learning curve on it can be pretty steep. Though not related to Python, the Unity3D Engine is also a popular choice among developers.
I'll be off the grid for a few days, but the important thing in all this is to find a platform you feel comfortable with and go from there, be it GameMaker, Unity3D, Python, or whatever else. Feel free to experiment and have some fun. ^^