Once upon a time, when a man who had just celebrated his 50th birthday was forced to perform daring feats of physical heroism by circumstances beyond his control—a mulleted, wild-eyed Mel Gibson, for instance—it was reasonable for him to respond that he was "getting too old for this shit." Not anymore. These days it seems like no one in Hollywood is too old to be an action star. When Lethal Weapon premiered on March 6, 1987, Danny Glover, who played aging cop Roger Murtaugh, was only 40. In today's market he'd be considered an infant.

Critics have already commented on the rise of the Geri-Action Movie: "gun-filled punch-'em-ups with stars in their fifties and sixties." But for a long time these films weren't all that unique. They tended to feature older actors who'd spent their entire careers shooting bad guys and blowing stuff up: Bruce Willis in A Good Day to Die Hard; Sylvester Stallone (67), Jean-Claude Van Damme (53), Arnold Schwarzenegger (66) and the rest of the cast of The Expendables. Sure, there were more wrinkles. And more Botox. And more jokes about arthritis. But Willis starring in A Good Day to Die Hard at 58 isn't all that different from, say, Clint Eastwood starring in In the Line of Fire at 63 back in 1993. Action stars age. That's never stopped them from being action stars.

But over the past few years something has shifted in Hollywood. Now actors who weren't action stars in their youth are suddenly morphing into action stars in middle-age. The trend began in 2008 with Taken, a Luc Besson-Pierre Morel action thriller starring Liam Neeson as a former CIA operative in search of his kidnapped daughter. It received mixed reviews but surprised studio executives by raking in $227 million worldwide—ten times as much as it cost to make. Taken 2 followed in 2012; Taken 3 was announced earlier this month.

Neeson's career was transformed. In an earlier age, he'd been known for prestige performances in Oscar-caliber dramas such Schindler's List, Kinsey, and Michael Collins. But suddenly an entire B-genre sprung up to serve Neeson's new sexagenarian action persona. Think Unknown. Or The Grey. Or next year's Run All Night. The genre even has a name at this point: Neesploitation.

For now, Neeson remains the undisputed king of the mid-life action conversion. But other pedigreed thespians have recently begun to nip at his heels: Sean Penn in The Gunman; Denzel Washington in Book of Eli, Unstoppable, and Safe House; Clive Owen and Morgan Freeman in The Last Knights. This weekend, meanwhile, Neeson faces his most direct challenge yet when Non-Stop (a thriller in which Neeson's grieving, alcoholic air marshal is framed for hijacking the plane he's trying to rescue), goes head to head with 3 Days to Kill (a thriller in which Kevin Costner's absentee spy-dad struggles to reconnect with his teenage daughter while hunting down a German arms dealer)

Why are aging dramatic actors suddenly flocking to action movies? Why is Hollywood so eager to keep churning out Neesploitation flicks (with or without Neeson)? I have my own theories about this, but I decided that to really get to the bottom of things, I had to consult an expert. The expert, actually. Which is why on a recent Tuesday morning I gave Joel Silver a call.

Silver, it turns out, is the producer responsible for most of the movies mentioned above. Lethal Weapon. The Gunman. The Book of Eli. Unknown. Even Non-Stop. When it comes to action, he knows of what he speaks.

The sense I got from talking to Silver is that the Neesification of action movies is all about the audience. Or audiences, to be more exact. As recently as the 1990s, moviegoers generally agreed on what they liked to watch: certain stars, certain genres, certain formulas. But the Internet basically killed the monoculture. Today, everyone is a demographic; everything is a niche. So the studios simply can't rely on the same mass audience they used to. "For many, many years, the young male audience was driving the action movies," Silver explained. "And now they've found a lot of other outlets. I have a 12-year-old son. He'd rather be playing video games that going to the movies."

This kind of fragmentation has forced Hollywood to cultivate two smaller action markets—young males on one side, older males on the other—where one big action market used to be. Young males who came of age after the decline and fall of the monoculture don't have the same attachment to individual movie stars as their predecessors, which is why none of the recent Next Big Thing action stars—Taylor Kitsch, Henry Cavill, Chris Pine, Chris Hemsworth, Chris Evans, and so on—have really become old-fashioned box-office draws in and of themselves. (Q: When was the last time you heard someone say, "You've gotta see the new Chris Pine movie"? A: Never.) Instead, Hollywood uses these post-monoculture action heroes almost interchangeably—as figurines dropped into "a superhero film, franchise-starter, or sci-fi blockbuster where concept and brand outshine the leading man" because for young viewers concepts and brands carry far more weight than marquee names. Superman puts 18-year-old bodies in seats. Henry Cavill does not.

More mature moviegoers are different; they're still attached to certain monocultural stars. "I've worked with Denzel Washington, Sean Penn, and Liam Neeson on action movies," Silver says. "The reality is that the older male audience is happy to see these guys on screen. They want to see more established, well-thought-of actors in roles that have a little more action orientation." And so, Hollywood has reverse engineered another kind of action movie to cater to these older stars—and the viewers who follow them.

The rules are simple.

First, the Neesonesque action hero must convey some semblance of hard-earned depth, which helps older viewers identify. "A lot of Non-Stop focuses on Liam's face, and for that you want an actor who can convey what he needs to convey," Silver told me. "That he's a troubled character. That he has issues. I mean, the movie starts with a depressed, morose guy sitting in a car drinking booze out of a coffee cup that he's stirring with his toothbrush. They see him thinking. They see him trying to figure it out. And they go along with him."

In other words, it's easier to seem believably beleaguered if you don't look like a little boy?

"Right."

Second, older audiences have become accustomed to the twists and turns of dark television drama, which in many ways have replaced moviegoing for the 30-, 40-, and 50-something set. So don't treat them like idiots. "The word that we're hearing a lot in our research is predictability vs. unpredictability," Silver explained. "You watch shows like House of Cards or The Walking Dead and you don't know where they're going. And a lot of younger action films tend to be predictable. You know what's going to happen. Audiences are a little sick of that."

Finally, mix things up. "There's an old expression in Hollywood about dust actors and rug actors," Silver continued. "Cary Grant was the greatest rug actor of all time, which means he would do scenes inside. Interiors on a rug. Other actors like John Wayne or Gary Cooper, these guys were dust actors—actors who would play roles outside, in the dust, on horses, with a gun. But with certain older actors like, say, Robert Downey, Jr., you can do both at once. Sherlock Holmes is a rug film with a lot of dust action."

In the coming years, the Neesification of action movies will likely continue. In fact, I'm betting it will intensify. After all, young people aren't flocking to theaters the way they once did, and the last of the monocultural stars aren't getting any younger.

A few weeks ago, I attended an advance screening of 3 Days to Kill. Right before the movie started, a woman in her 50s sat down next to me. She asked if I was a journalist. I said yes. She looked as if she had something she wanted to confess. "Here's the thing," she finally said. "I've gotten to the age where I don't know the names up on the movie posters anymore." She paused as the lights began to dim. "That's why I was excited to see the words 'Kevin Costner' up there the other day," she told me. "At last—a name I recognize!"