My kid is about the same age. We recently bought a safety lock to prevent him from getting into cupboard under our sink. It had great reviews on Amazon.
The first time he went into the kitchen after I had installed it, he notices it immediately, walks straight up to it, grasps it with both hands like an adult would, and has it unlatched within 5 seconds. He then proceeds to look at me like "Is this some sort of test?"
The first time he went into the kitchen after I had installed it, he notices it immediately, walks straight up to it, grasps it with both hands like an adult would, and has it unlatched within 5 seconds. He then proceeds to look at me like "Is this some sort of test?"