Definitely, a highly gifted child should be allowed to skip grades. It is tantamount to child abuse to have a gifted children not skip a grade. If a highly gifted child is forced to remain in a normative grade, he/she will become bored. Also, a highly gifted child will be bored with same aged peers. It is better for the child's intellectual development to permit him/her to skip a grade or two or three.
Better yet, if there is a school for highly gifted students or a gifted program within the regular school, enroll him/her into this gifted program. Highly gifted children need to use all of his/her intellectual potential. So many parents and our antiquated, backward educational system are loathe to let highly gifted students use their intellectual potential in favor of "being normal" which is a severe disservice to the student. Place the student in an environment when he/she will INTELLECTUALLY SHINE!