Unused engine oils in sealed containers have a shelf life of maybe 2-3 years? It's when you start using them in your engine that they start collecting contaminants like diesel, soot, watervapour and they all start breaking down the oil from day one, forming acids, sludge and what not. Regular mineral oils also start thickening like varnish if you let them sit for longer periods of time. So not driving the car that much, will actually wear down the engine quicker, cause the oil no longer lubricates efficiently, being thicker. Heavy use, in terms of mileage, keeps the oil moving and delays this process somewhat. But then the oil will start breaking down from high heat and faster collection of contaminants. Toyota have done their research, but knowledgeable people on here have their own experience to show for. Trust in that