Can't install python-dev on centos 6.5

On CentOS, the python development libraries are under the name python-devel, not python-dev.

So you should use

sudo yum install python-devel

to install them on your CentOS system.

You can search the repositories available to you using the yum search xxxxx command, where xxxxx is the name or part of the name of the package you are looking for.

Further, you may need to specify the architecture (such as python-devel.x86_64), although in my experience yum will automatically install the package that is appropriate for your system. Again, yum search will show you what is available in the repositories you currently have installed/enabled.

Did you try

yum groupinstall -y 'development tools'

Did you try to download the RPM package and install it?

Did you try to install python-pip then issue pip install python-dev?