I wouldn't hold back gifted kid because of maturity. Think of it this way.. instead of worrying about next year in K. What is he going to be like in High School a year older than most of his peers. Years ago when I was looking at sending vs. holding back my DD. (I didn't and later regretted it but she isn't a gifted kid and struggled academically) I read research that showed problems with 18 year old H.S. seniors. who had been held back in Kindergarten, particularly boys. These kids were more likely to mentally check-out and not meet up to expectations, and get into trouble.
