aside from limitations like, you can only setup 1 app, or things like 2f authentication. Usually things like this are stopped by laws and enforcement causing consequences. I'm pretty sure that sort of thing would be considered identity theft. same thing as stealing their father's drivers license and opening bank accounts in their name.

There are physical barriers and there are barriers that are enforced manually. Same with speeding. you are not allowed to drive faster than 60. even though your car can drive faster, laws in combination with police, traffic cams and speed traps will make sure it's enforced.