My 2018 was also an Ichiro fan. We used to live in Seattle, and that was the first player he ever followed. Small(5'9", 165), but very athletic and coordinated. From the time he was 15 till the summer between Junior and senior year in HS his OF velo went from 81, to 86, to 91mph. A lot of it is technique. He uses his quick twitch legs to hurl himself in the direction of his throw, almost like he is thrown out of a cannon. All his momentum seems to aid the path of the ball. Since he has gone to college he has added more "good" weight(185 now), and has hit 94-5.
I would disagree that hitting 90 doesn't attract attention, even if it's from the OF. As soon as he did, he started to get a LOT of attention from schools. Not P5's or anything, but smaller schools looking to convert him to a P.
He started to play long toss regularly from the time he was 16. That's where you can build up arm strength, and work on technique, and coordination. He and a teammate(a P5 recruit) used to throw foul pole to foul pole after practice for about 20 minutes.
I also have a 2022, but he is blessed with good height, though he is still wiry. He was a P/OF, had elbow problems, and had to completely reinvent himself after it was determined that technique was the problem rather than structural issues. Long toss has been part of his new regimen. Last fall he was maxing out around 240', with pain. Now, he can throw around 320'. No idea what his velo is from the OF...I do know that his technique is not where his brother's is. I would guess he would top out around 85...is 81 from the mound? In both places, his technique is probably hampering him. Strength is great, but it's all for naught if you don't have technique, and your body is fighting itself. Talent is another thing, too...some guys just have it.