ATC=Air traffic Control.
ATCO=Air Traffic Control Officer.
I'm sure you could pull people off the street and make them into controllers... just like you could make them 747 pilots, doctors, scientists, racing drivers, etc! Well, one could dream.
There are certain qualities which most ATCOs have which are not related to education or good health; it's just some strange quirk which allows them to do a job which others cannot. Even after extensive training I've seen controllers fail to make the grade; they simply could not hack the operational task. It's possible to teach someone how to behave when things go wrong, but would they actually manage? I used to impress upon trainees to make a concerted effort to speak slowly in an emergency. It gives one just a few more microseconds to think, re-assures the aircrew that they are dealing with a professional and should remove the need for "say again" from the pilot.
Good luck with your application. If you make it, listen to those training you because they know what they are doing.