How long would it take me to learn c++ and make a 3d shooter app with physics and blood lots of details??

depends how much you know now

2 years... ^_^

If you learn to code, you will also need to learn how to make the graphics :P

when you come to the point where you know all that stuff you will want to make your own OS

Dont try to reinvent the wheel as it sounds like.

this days its not really hard since there game engines, just look for one that uses c++ like panda 3D...but for how long it will take you to learn depends on your determination and whether you are a fast learner or not