La Texican,
Your DS sounds somewhat like my DD. She is SLOW. She does everything slow. Brushing her teeth, taking shower, eating, etc.... We have to wake her up early so that she could be ready for school. It takes about 30 minutes for her to go to bed (just brushing her teeth and using the bathroom). But she finish her multiple choice questions quick. She is a perfectionist so she would take her time to do writing, projects, etc...
She skipped K and went straight to 1st grade. May be what your DS experiencing is boreness not the maturity. Ask your district about the policy to skip a grade. Usually recommendation from the teacher carries a lot of weight but probably not in your DS's case.
Good Luck!