How old is Jonas? Why is he apprehensive about the month of December

Jonas is just about to celeberate the Ceremony of Twelve, so until that day he will officially be an "Eleven". Jonas corrects his initial feeling of being frightened and replaces it with the word apprehensive, as in December, at the Ceremony of Twelve, he will receive his assignment.

He had waited a long time for this special December.
Now that it was almost upon him, he wasn’t frightened, but he was . . . eager, he decided. He was eager for it to come. And he was excited, certainly. All of the Elevens were excited about the event that would be coming so soon.
But there was a little shudder of nervousness when he thought about it, about what might happen.
Apprehensive, Jonas decided. That’s what I am.