I don't know what Florida law is with respect to self-defense, but here in Ohio, self-defense is an affirmative defense. I've prosecuted these kinds of cases. In essence, what the defense has to do is say, meaning that Z would have to say "Yep, I intentionall shot him, but there's a justification." It then becomes the burden of the defendant to prove that the shooting was justified. That's where this case will get interesting, assuming that the defense chooses this strategy. Why? That's where all of the crap about who did what first will come out.
In my opinion, under Ohio law (again, don't know Florida law), there's one key issue...in Ohio, the person claiming self-defense must prove that he was not responsible for creting the situation in which it became necessary for the deadly force to be used. Classic example from the past was a man who broke into a house, aremed with a handgun. The homeowner finds the crime going on, and comes at the burglar with a bat. Burglar shot and killed the homeowner. At trial, he argued that he reasonably feared for his life and only fired to protect himself. Because he created the situation b y breaking into the house, the justification failed. If Florida law is like this, Z has a problem, in that he created the situation by following T in his car, getting out of the car, and pursuing T between houses. And, this testimony will be the key point when the prosecutor can play Perry Mason during Z's testimony (and he will have to testify if he's going to claim self-defense). When he says that he was afraid for his life, the prosecutor will say "at what point, Mr. Z? When you followed him in your vehicle, or when you left your vehicle and chased T on foot? Or was it when you had him cornered, and the boy saw no choice but to fight back against someone he believed was out to attack him? If you were so afraid, why did you ignore the directions of the police dispatcher and chase this boy?" If it gets to that point, that is where Z will lose. Yes, the Stand Your Ground law may say that you don't have to retreat, but it isn't a license to engage in a pursuit.