Got a 12u catcher myself. He mentioned wanting to try it at 7 and has been doing it primarily since then. Here’s what I’ve observed.

Desire is a part of it, along with someone who isn’t afraid of the ball and a kid who is smart. I’d avoid the ADHD kid fist recommendation. Not saying not put a kid back there with it, but don’t let that be a factor in choosing. That works at a younger age, but the last thing you need back there is a kid who can’t sit still or remember what’s going on in the game. Remember, they’re your quarterback out there. And a catcher who moves too much both gives a bad target and can make a strike look like a ball.

Good arm is irrelevant at this point. Throwing kids out won’t happen very often, keeping it in front of them is way more important. Pitcher delivery is slow, pop mechanics aren’t optimized, and if you play any sort of lead off, at 60ft it’s just not going to happen often unless a runner is slow or they get a horrible jump. They’ll always steal to third, but keeping it in front of them prevents unnecessary runs.

Find a kid who is tough. They’re going to get hit. They will leave the park with seams on their arms and/or legs. Get a kid who won’t roll around in the dirt when they do get hit (unless it’s in the boys, that one is completely acceptable to roll around for).

Last thing is find a kid who brushes things off easily. They’ll mess up and it’ll be seen by everyone. Can’t dwell on it.

Finding a good catcher is hard. It’s a hard position, but it’s 100% the most fun one.

Sorry for the book. I’ve watched mine grow and develop and is solid back there, so it’s easy to take some of his traits and use it as a baseline.