My son's kindergarten class has several 7 yr olds in it.
So what, I was 12 going into the 9th grade in public school. When I went to private school, I repeated (red shirted) the 9th grade to attend my preferred school (they did not take kids into the upper school). I turned down Exeter, Andover and Mount Hermon which accepted me for the 10 th grade. I was still the youngest in my repeat 9th grade private school class. No issues. I was the shortest and lightest when I matriculated. I ultimately played 2 varsity sports and captained the basketball team my senior year.
I was not intimidated intellectually, athletically, creatively by older or bigger children (nor smaller or younger children). My parents did not instill these crass notions of inferiority in me as a youngster.
The proper fit does not necessarily adhere strictly to chronological age.
This parent is making a mountain out of a mole hill. If you do not like bigger, older...or smaller and younger children, in class with your child I would suggest withdrawing your child from the school.