I think that guy is lucky your dad stopped.
Last "old fart" ex-marine I saw get into a fight nearly killed the punk.
He was nearly 70, and the punk was trying to rob the liquor/grocery store he was in.
He ended up shooting the kid with his own gun in the shoulder(after tackling and beating him a bit), and kept him there until the cops arrived.
Marines KICK ASS at any age.
Yet another "thanks for serving" from me to your old man!
L8r