Also if it interferes with your health, and a few other things. If playing video games takes precedence over, say, taking regular showers, or even basic exercis

Also if it interferes with your health, and a few other things. If playing video games takes precedence over, say, taking regular showers, or even basic exercise? I'd call that a mental illness too. But I agree with the main point: “person wants to live in a way I don't like” is not mental illness.