And the reason why this matters is that the dating that matters is the dating from when we can have children to when we're done. So if a woman starts seriously dating at 20, and is done with kids by 35, then somewhere around 25 is indeed the proper cutoff.
Men can have children longer, but at some point don't want to.
Whatever you personally think, you're dealing with a lot of biological wiring which is intended to optimize your life towards the goal of having children successfully raised to adulthood until they also have children.
This wiring does not work with all individuals nor can it always cope with modern life. But it is still a pretty big factor.
I would guess I had done 36.8% of my dating by age 25 - not 39. Suddenly the model starts to fit better.