We have four as well, and coincidentally our oldest is 22. He is doing well - still thinks he is the alpha of the area, even though he has no upper canines (well few teeth full stop), has limited vision in his left eye, one kidney and is on daily heart and blood pressure medication. You wouldn't know it at times. He doesnt sleep much at night and doesnt particularly enjoy his renal diet but he is a big personality and a huge part of our lives.