I don't change the oil all that often (maybe every 8000 miles) and on my 10 year old car the oil light comes on and I need to add a quart or two (and then I start thinking I practically changed the oil and don't need to worry for another few thousand miles!). Does that mean it's leaking for sure? Or does oil make it's way though the pistons in an older car and burn off in the combustion process?
Note there are no (new) spots on my driveway.
The oil is most likely being burned by the engine. You should change your oil more often, it's not just new oil you are putting in, when you change your oil, it takes the old oil and contaminates suspended in that oil out. So by added 2 new quarts every so often is not nearly the same as changing the oil.
Also I would recommend checking the oil level on a regular bases, if you are waiting for the oil light to come on that means there is not enough oil in the pan for the pump to pick up. Oil lights come on around 8 psi in most cars. If you are waiting this long you could be damaging your engine because the oil pressure is too low. Now in the event the light you are referring to is an oil level light you might be alright as far as the oil pressure goes.
The oil is going somewhere. If your vehicle is not marking its territory (leaking when parked), it's probably burning it.
