I don't see him getting life in Florida. (Full disclosure, I was born in Florida, lived and worked there a good portion of my life, have family there including in this area and a brother on the bench in another part of the state.)
It's definitely a possibility, but if I had to bet today, I wouldn't go that way.
Placing the line in this case is going to be difficult... or lines, I should say, because there's more than one.
GZ was within his rights to carry a firearm, within his rights to be in a neighborhood watch, and within his rights to walk up to someone who's also walking in his neighborhood and ask if he lives around there, and quite frankly also within his rights to be an ******* about it.
And this is true, even though the dispatcher told him that "we don't need you to" go walking up to TM and talk to him. GZ wasn't told not to do it, just that it wasn't necessary. This kind of detail becomes extremely important in trials, where juries find themselves having to consider everyone's plausible point of view as things unfold.
TM was within his rights, of course, to be walking down the street with a bag of skittles and a can of AIT with a hoodie on in the rain.
He might have been something of a punk, but even if so, that's not anything GZ would be aware of, and his claim to 911 that he believed TM might have been "on drugs" is suspect at best, but maybe he believed it.
So now we've got a situation where both parties are plausibly acting within the law.
Whatever happened out there on the sidewalk that night, we've at some point got 911 calls from neighbors about a fight, someone's hollering, there's a gunshot, and the hollering stops.
By all accounts, GZ initiated the contact, and did nothing illegal in the process. They argue, also not illegal. Then a fistfight breaks out.
The SYG law can now be argued both ways.
TM is not here to give his side of things, so we cannot discount the possibility that he might have testified that GZ initially turned the argument into a fistfight... and since GZ is much larger than TM and was pursuing him and was armed, and was complaining about how they "always get away", that's entirely plausible... so despite GZ's tesimony, there's reasonable doubt about who started the fisticuffs.
So let's say it was TM. There's reasonable doubt, so we presume innocence and hypothesize that it was TM who punched first.
There are now 2 questions in play:
1. Does TM have a SYG right to stand his ground and attempt to disable GZ if he believes GZ is an immediate physical threat to him? (And it's hard to imagine that any 17yo his size would not perceive GZ under those circumstances as a threat.)
If GZ is justified in shooting TM, then by their own argument, they're admitting that TM had a right to attempt to physically disable GZ.
2. Does GZ at that point have a SYG right to stop TM from beating him?
Well, by the same token, if it's reasonable to believe that TM had a SYG right to attempt to disable GZ, then the same must now be true of GZ with respect to TM.
And that's what makes this a tricky case.
You mention life, there's also a potential for an acquittal for precisely these reasons.
My guess is that the deciding factor will be the fact that GZ initiated the confrontation, with a loaded weapon at his disposal, in a manner that was likely (and indeed calculated) to make TM fearful.
So a conviction, but manslaughter, less than life, because it was in some way reasonable for GZ to have a good faith belief that he was acting legally, given the actual language of the law -- if it takes us this long to hash it all out at leisure, how can we expect him to parse it in a few minutes?