I'm going to get a group of old people kicked out of the gym
Why are you going to get them kicked out?
Because my father is afraid of the other old people in this place.
I'm not sure why your father is afraid of the other old people, but you shouldn't try to get people kicked out of places for no good reason. Instead of trying to get people kicked out you should discuss the issue with them directly.
We both think they're creepy and they always lurk near the machines and I want them gone.
It doesn't really sound like they are doing anything that would justify you getting them kicked out of the gym. Can't you and your dad just ignore them? Perhaps you can just put on headphones and focus on your own workouts.