Part of the magic of Hollywood movies is that the larger-than-life heroes and heroines up there on the screen don't age and wither and deteriorate like the rest of us do. In fact, it may be that one of the reasons we go to the movies, at least in youth-obsessed America, is to bathe in a cinematic fountain of perpetual youth. If they're not getting older and flabbier, maybe we won't either.
The bargain we seem to strike with the movies is that if they keep our screen gods and goddesses free of age and blemish, we'll continue to adore them and shell out money to go see them. As the movie audience grows younger each year, the last thing they want to see is a bunch of old farts with bald heads and beer bellies up there huffing and puffing around on the screen. So it seems only logical—indeed, financially imperative—that the people who impersonate these heroes for us shouldn't age and bloat and wrinkle. By and large, the last thing we want is for our aging movie heroes to act their age.
One of the wonders of modern entertainment is that we always have our store of old movie memories to fall back on. So when Sean Connery moves into his fifth decade of stardom, seducing all the women, killing all the men, and blowing up all the buildings without wrinkling his tuxedo, we're happy and find our own feeble powers correspondingly enhanced. When we see Gene Kelly dancing with his grin undissolved by the rain, some part of us—however decrepit we may be—keeps thinking, "I can do that, too." When we gaze enraptured at Ingrid Bergman, with her eyes glistening at Bogey, as luminous and dewy as she was the last few hundred times we've seen that scene, we know, in our infatuation with her flawless loveliness, that we'll remain young forever.
But the gender rules for aging in the movies are far from fair. While the powerful men that rule Hollywood and make the casting decisions may overlook their own age and state of deterioration when casting male leads in romantic roles, they don't grant such passes and bestow such kindnesses upon aging actresses. As actresses approach 40 (even marvels of youth and beauty like Julia Roberts and Gwyneth Paltrow), they tend to fade from the screen, while old men on screen still get to flash their worn charm. Audiences often go along, tolerating certain aging stars out of a primitive loyalty to the macho invulnerability we admired in our youth.