I have no issue with the age approach, but only after one is assured that the two parties have a reasonable chance of building a bayis neeman together. By limiting one’s shidduch pool to this somewhat narrow window, one is not necessarily ensuring this.
There are so many deeper problems that intersect with the shidduch situation – kids dropping out, financial issues, kavod rabbonus and infrastructure,developing good, solid kids for starters – and focusing on age as the magic bullet strikes me as superficial and facile. I guess I’m missing something.