It seems pretty age-normal for me for a 6-year-old to have difficulty managing his time when he finishes his work. Does he have other social delays or impulse control issues?
FWIW, My 2E (ASD/ADHD) PG DD is in the age-normal grade. When teachers didn't take this into account, we had lots of behavior problems. She's now working a couple grades up in math and the latest reporting on reading comprehension put her instructional level in high school, so it's all quite easy for her.
So, academically she could move up a couple grades. But I think since she's 2E, over the long run it'll be beneficial for her to have more time, not less, to develop organizational and communications skills, self-control, and self-motivating skills essential for success as an independent adult after high school.
