Depending on where you live, there are plenty of 16 and 17yr olds that will back their shit up. From what I have experienced, if teens, or anyone for that matter, talk a bunch of shit to someone they dont know, they are either a bitch or a really tough cookie. But more often than not they are a bitch.
So as everyone else in this thread has said, I believe 100% that the kid wont do shit.