AZ a couple of points:
1) I didnt choose to define the crises that way that is often how it has been presented, see the above lengthy article DY quoted and catch the author doing a bait and switch.
2) I outlined above shiduchim is a process, a leangthy one at that It goes something lke this “shadchan suggests girl, boy’s side looks into her, Boys side agrees, girls side looks in and agrees, they date, get engaged and married” To analyze the “crises” We have to see where in that line is there an oddity, where are people being left behind? Are the boys not hearing of them? That does not seem to be the case. Most boys I know/knew have long lists of available girls. On to the next step are many girls not being chosen to date? By asking around yes this seems to be where the disparity lies. Some girls have plenty dates while others, to quote the above cited piece, have “relatively infrequent dating” This is the casue of the “shidduch crises” and it cant be explained by “age gap”
MArrying girls several years younger is not new, increse in population is not new either. The “shiduch crises” is new. Therefore some other new societal changes that did not exist 15/20 years ago have caused this situation.