Still doesn't justify it. Florida law says that you have to be in iminent danger of death or great bodily harm before using deadly force. There is no way that your scenario could fall under that.
If you are a 71 year old man holding a 43 year old man at bay with a gun and the younger man (who is only feet away) tells you he is going to take the gun and shove it up your ass and then moves toward you, you wouldn't feel in imminent danger?What do you think happens when he gets his hand on the gun?