To my understanding, disparity of force is a valid defense. The septuagenarian is not expected to grant as much room, leeway or ground to the predator as the 25 year old martial artist.
By way of example, an opponent on the opposite side of a parked vehicle, brandishing his belt, is probably not sufficient threat for you OR that 74 year old to let lead fly. But once he begins advancing around the vehicle, you'll probably find yourself held to a higher standard than Powderkeg.
And that is.....
as it should be!