Gran Torino/WMG

Walt is really The Man With No Name.
Or one of his descendants. Both are assholes and retired badasses. They both go out of their own way to help out someone that needs it. I believe its the former, because many of the Characters Clint played in his westerns seem to be older than they appear. During the climax he makes a remark that the Big Bad is a miniature cowboy when he and his friends have their guns ready at him. To top it off he is able to intimidate most people without ever having to fire a shot. Last but not least unless he was planning to die anyway  he would never lose a duel. Personally I think this was the final chapter of the Dollars series.
 * And that also ties into Unforgiven.

Thao joins the Army when he turns 18
Alternatively goes to college, and joins as an officer
 * That would actually be a good idea for the sequel if they ever make one.
 * What? That's a terrible idea, how would that be good sequel material? The entire point of the ending was teaching Thao that violence begets violence, and that war scarred him for life. Why the hell would Thao up and join the army in any capacity?
 * Attempt to end violence for other people?

The granddaughter tries to get that Gran Turino from Thao
And she fails! Or she falls in love with Thao. Admit it, that would make a neat subplot for a sequel.