The problem with the mbsarcha al tisalam argument is that we’re not dealing with tzedaka. We’re dealing with setting two people up to build a bayis neeman beYisrael. And if something in a shadchan’s mind clicks, and it’s outside the narrow age limits, what’s s/he to do?
Also, it’s all well and good to quote a certain gadol that the problem exists. I have yet to see a gadol come out and give clear guidelines, other than joining a NASI endorsement list.