Just to add to the general consensus. In your situation, I think we would be opting for the extra year. Time to mature, develop confidence, skills, etc.
We did not hold ShawSon, who was/is dyslexic, had a speech delay and a bit of ADHD thrown into the stew, back in any way because he was so ridiculously bright that he was bored with school curriculum. We did bring him to a private school in 3rd grade that specialized in dyslexia and related issues for summer school and asked about enrolling him and they said he was too bright and they worried he would be a behavior problem. But, he took a gap year before college and was really happy he did so. He was a nerd with well-developed social skills (learned/inherited from his mother) and self-confidence was never an issue.
We think ShawD would have benefitted from an extra year at some point. She was a summer baby and was always the youngest kid in her class. When she switched to private school for middle/high school, she was often one to two years younger than many of her classmates. Following ShawSon was a bit difficult for self-confidence. Although he struggled with reading/writing, he was making change in Monopoly before he went to kindergarten and intuitively understood exponents in 2nd grade and generally was strong at anything that involved conceptualization. So her confidence was not what it should have been. And, classmates who were older also had a similar effect. Indeed, both at the very selective middle and high schools she attended, she gave the impression of someone who was not strong and her advisors were surprised that she was much nearer the upper end of her class than they would have expected given her self-confidence level. We suggested a gap year but she really wanted to get on with life and get to adulthood as fast as possible. In her sophomore year in college, she really gained self-confidence. So it all worked out. But, I think a year before HS or a gap year would have been good for her.