On the subject of Yu, another guy who’s had velocity gains into his 30s is DeGrom, only his have been much more dramatic. He’s in his age 32-33 season and averaging 99.3 on the fastball, after having been in the 93s a few years after TJS.
I have no idea if he’s one of those guys using sticky stuff - presumably yes, since they pretty much all do. But that wouldn’t explain a guy consistently adding major velocity well into his 30s. I don’t know anything that does explain it, honestly. But it should be getting more attention that he’s having possibly the most dominating season by a starting pitcher in MLB history.