Short answer is, the data is mixed. I think the Locke has a point. I think Locke's critics have a point. But generally I think Locke is more scared about Kaminsky than he needs to be.
My beef with Locke is not with the age thing, at least not directly the age thing. I think he is prejudging him based on the age thing and when I say prejudging him, I mean - he's decided that he doesn't like him based on the age without ever watching him or scouting him extensively and now is fabricating and propagating false narratives about him to support his prejudgement(i.e. he's a ball-stopper, he doesn't move the ball, holds the ball too much... like what the actual f**k?!?, his release is slow and he won't be able to get it off in the NBA, etc.).
The age thing is a real concern, but shouldn't be a disqualifying factor in our consideration of Frank.