My son was actually a YNT finalist twice, at ages 15 and 16, but failed to make the final cut both times. When he was 15, he was topping out at 89, but when he got to trials he was simply not ready for the caliber of hitter he saw there. His location and off-speed stuff weren't at their level. When he was 16, he hit 93 in Jupiter, and his command and off-speed stuff were much improved. But then he had a foot injury that threw him off his preparation schedule, he had a bad outing at trials, and that was all she wrote.
So, to answer the question about pitchers' mph, let's put it this way. High mph gets you noticed. But it isn't the only way to get noticed. And it isn't enough to get you all the way there.
There were two 90+ guys at trials last summer. Both were cut from the final squad. Neither one really had a good week at trials, my son included. The competition was keen and he had one bad outing, one good outing -- not good enough.
It is tougher to get noticed when your max speed is below, say, 86-87 mph. But not impossible. Weber was 81-83 in the game where he snuffed our team but good. But USA Baseball watched every pitch and learned what he had that makes him special.
What I would say is that if you are not a high mph guy, it can be tougher to stand out in a crowd. But the record shows that those who have something else special can and will get noticed. When you're facing a team that's known to be tough and you are putting them down inning after inning, somebody will take note.
On the other hand, high mph alone might get you to trials, but not necessarily all the way to the YNT roster. I guess you can't make the team if you don't make the trials, so high mph is a big plus. But you still have to get elite batters out to make it. And trust me, you will see some of the nation's best young hitters. The trials are probably tougher competition than the tourney itself!
I think also that last year's YNT coaches intentionally de-emphasized mph in favor of "feel for pitching". Given the way they stomped on everyone, including Cuba, to win the gold, you can't argue with their approach. And it's yet another reminder that we often place too much emphasis on high mph.
It can be a gift, but it isn't enough to succeed, and it isn't the only way to succeed, either.
My advice: If you really want to stand out at JO's as a pitcher, ask your coach to start you against your team's toughest opponent. If he does, the rest is up to you. If he doesn't, then maybe he's telling you that he doesn't think you're at that level. In the end, if you don't have your own coach's support, you're pretty much out of the running.
P.S.
The mph numbers above are MAX numbers, meaning the highest fastball registered during the tourney. Typical speeds are going to run 2-4 mph lower. Don't confuse the two.