I saw it tonight as well. Overall his performance was very good. I agree he came off as very young--much younger than I would think of for the King. I also think because he is physically smaller he didn't have the kind of command of the stage or presence as I imagine Ken Wantanabe must have had (although I didn't see it with him). He didn't seem intimidating to me. However, obviously his size is not within his control and I don't mean to diminish his performance. I thought it was a beautiful show and he did well in it--it just wouldn't be my dream casting. He has a beautiful voice and acted it very well--he was funny in all the right parts. I very much enjoyed his performance and I would not dissuade anyone from seeing it with him.
Obviously Kelli and Ruthie Anne were AMAZING. If I had to pick between waiting to see it when Ken Watanabe comes back but Kelli might be gone, I'd prioritize seeing Kelli in this role because Jose was certainly enjoyable to watch and did a great job.