True if ALL 23 year olds only married 19 year olds there would be a problem.
Maybe this is the point we differ on. You say that if a small amount(e.g. 5%) would marry at the same age, it would solve the disparity issue. I say it will help, but not solve it. (Also there are those who marry at a bigger age discrepancy than 3-4 years which makes it worse).