I think his arm length is more important than his total height. There have been some really good tackles that don't have ideal height but they're able to make up for it with their athleticism, reach, and technique. But in saying that it's really hard to less than 6'4" and be a successful tackle, so if he's not at least 6'4" (I think he is that tall btw) I totally agree with you.
Yeah, I'm not saying he couldn't be a Tackle currently, but as young as he is, it's possible there's some growth there yet, and it certainly wouldn't hurt.