Read the letters carefully. The only ones signed by recognized gedolim say that there is nothing wrong with bochurim dating girls closer to their age. And you know what? They do!! All these people that say there is an age gap because 23 year old boys marry 19 year old girls has an exceedingly closed mind about how statistics work in the real world. They have no understanding about the fluid nature of the shidduch market; what brings people in and what takes them out. Most shidduchim are redt and most marriages are between people of closer age than 4 years. Just because a boy starts at 23 and a girl starts at 19, doesn’t mean that every, or even most shidduchim have a 4 year gap.
There are so many factors in our community that can increase or decrease the flow of bochurim and girls. Analyzing cheder statistics is an unbelievingly shortsighted and perspective-limiting method of determining what happens in the shidduch market 10-15 years down the road.