Hides long list of ethical problems with the concept
Men are (within reason) considered handsome in media even in old age. Wrinkles and gray hair can be seen as sexy (again, within reason), but only in men.
Women are discarded or relegated to sexless granny roles (except maybe for comedic purposes, where sexuality is the butt of a joke). Actresses are replaced by younger women because they are not sexy enough even when their male equivalents aren't (looking at you, Top Gun: Maverick).
I'm not saying there aren't exceptions in particular movies that deal with this topic; I'm talking about the general trend.
The reflection of biological reality appears easier to justify: that men remain fertile for longer, that the attractive qualities that women care about most (e.g. wealth and personality) tend to improve with age; and that a women's attractiveness is most tied to her skin, which we all know shows aging the most on the body, and is a sign of her reproductive health or ability.
I'm not sure what the argument for the media being able to influence males to the extent suggested would be? Older men were marrying younger women before the printing press, so where did this pressure originate? And what is its mechanism of action?
I'm saying media could be changed from this tendency, since this preference is less relevant in modern society and it hurts actresses. Media is a human construct that can be adapted to new needs, it's not a tool of natural selection!
Changing media wouldn't change the sexual preferences of men, and nowhere am I arguing this. It's like inclusivity in media -- is it ever going to eradicate racism? No, but it will make the world a tiny bit fairer.