My cat was a grazer and hunter
My sister's cat would eat everything, including everyone else's (but would never mouse, bird, bat, bug... he only ate food that was already dead. Even if he killed something on accident he just looked at it helplessly. Like a kid with a broken toy). He'd eat, and eat, and Eat till he made himself sick. (My dog does this now, I'm convinced it's karma, because I looked down my nose at my sister for her cat's behavior! Ouch. Thanks karma.)
They each lived nearly 20 years... and no change in either of their habits.
One idea, which we didn't do, (because I just thought of it)... are those magnetic collars that open cat doors. If you had a room with food in it for older kitty, and her collar opened the door, it would be a retreat, and you could just leave her food down on the floor for her. Of course, she might let Jr. in. But it's the only way I can think of to leave food out and not have it be scarfed by the wrong cat or be bouncer/maitre de feline