DS is the same age and also loves to throw objects. I do allow him to throw balls (soft ones) in the house though, so I gently take the object that he is about to throw away and say, "we don't throw ...., that could give someone an owie, but we can throw balls. Do you want to find some balls to throw?" He usually does and doesn't seem to mind that he isn't allowed to throw forks across the kitchen table.