Wait until he is 9th grade. 18 months is nothing.
Are you trying to rationalize or build on the age discrepancy further? I can’t tell.
Then I worded my post perfectly.
He is a holdback apologist. 18 months becomes less and less as children age. A fifth grader looking at 6th graders is a whole different ballgame than a 10th grader looking at a 11th grader. Common sense.
That holdback argument is just as good as, it will make your son better going against holdbacks, while they play down a year.