A litter box for elderly cat needs to be as easy to get into as possible — and that starts with a low entry point. Older cats, especially those dealing with arthritis, extra weight, or coordination issues, can struggle to lift their legs high enough to clear a tall side.
Spaciousness matters just as much. Your cat needs to be able to walk in, turn around, and dig comfortably without feeling cramped. A box that's too small often means the cat ends up half in, half out — and that leads to misses and mess around the box.
A good elderly cat litter box should also be stable. It shouldn't slide across the floor or wobble when your cat steps in, because that kind of unpredictability can put an older cat off using it altogether.