Why is Kuja such a noob?

[The Crystal]

He obviously new about the Crystal ahead of time, as he knew where to go to find it, so he had knowledge of it.

Whether or not it is possible is up for debate and theory, but it's obvious as even if it is possible, Kuja didn't know how to do it.

Due to the limited time he had to live because of Garland, it's most likely he didn't have the time to learn how to use the crystal if it's even possible.

So basically yes, he knew he couldn't use the crystal. Nothing in the game even points to the possibility of mortals being able to use the crystal anyway.

I was going to say that there was no way Kuja knew it wasn't possible to use the Crystal, because there is no evidence that he ever came in contact with it and tried to do that, before that moment in his life. But... You made a good point in the first sentence of your thread. "he knew where to go to find it". If Kuja knew where the Crystal World was located and how to go there, then there is a good chance that he already came in contact with the Crystal, and knew it was "useless".

Yeah, you can be right.