The great fictional detectives of the last century seldom aged and almost never died.
There were exceptions -- Sherlock Holmes and Mike Hammer both (apparently) died, when their creators grew tired of them. But when the public demanded, those deaths became as exaggerated as the reports about Mark Twain's passing (you remember Twain -- author of Tom Sawyer, Detective?).
You can write if off to simpler times, but it makes good storytelling and commercial sense even today to keep popular detectives frozen in amber. Readers of series fiction come back to spend time with characters they know, familiarity breeding not contempt, but comfort. None of this character growth stuff, and a hero dying? Out of the question.
Agatha Christie cheerfully ignored Hercule Poirot's obvious old age, and wasn't Miss Marple born a spinster? Of course, Christie prided herself on unpredictability, and she did kill off Poirot, but only in a novel she squirreled away in a safe-deposit box, for publication after her passing. Maybe it says something that Miss Jane Marple does not die in her similarly set-aside final series entry.
Erle Stanley Gardner not only kept Perry Mason frozen for 40 years, he depicted Los Angeles in as non-specific a manner as possible, keeping not only defense attorney Mason, super-secretary Della Street, and indefatigable PI Paul Drake ageless, but the world around them, too. Gardner wanted to keep the novels timeless, so they could stay in print forever -- for many decades, he got his wish.
Teen detective Nancy Drew stayed static as well, although those who controlled her destiny began in the late 1950s to update the older novels and their illustrations, removing for a lot of readers the charm of their 1930s origins -- running boards, seamed stockings and all.
Perhaps the most eccentric approach can be found in Rex Stout's wonderful Nero Wolfe and Archie Goodwin series. Stout kept Wolfe constantly in his mid-fifties and Archie in his early thirties, though the world around them changes, from a post-Prohibition setting in Fer-De-Lance (1934) to J. Edgar Hoover's decline in The Doorbell Rang (1965). The final few novels even include references to Vietnam and Watergate. Most outrageously, a character from Too Many Cooks (1938) returns 26 years older in A Right to Die (1964), while Wolfe and Archie remain untouched by time.
Mickey Spillane did not shy away from making it clear, even in novels written in the '70s, '80s, and '90s, that Mike Hammer was a proud veteran of World War II. He avoided stating Hammer's age, however, and dealt metaphorically with issues of aging by beginning several novels with a weakened Hammer. In The Girl Hunters, Hammer has been on a seven-year bender; in Black Alley (1996) and the posthumous Kiss Her Goodbye (2011), Hammer returns to New York after recuperating from near fatal wounds.
In the current King of the Weeds, which I completed from Mickey's partial manuscript and notes, Spillane more openly addresses the passage of time. Both Hammer and his cop pal Pat Chambers are facing imminent retirement, and the case at hand has roots in the start of their careers.
The successor to Spillane's crown as king of private eye writers, Robert B. Parker, followed Stout's lead and his detective Spenser, a Korean War veteran, was kicking bad guy butt well into the twenty-first century. Sue Grafton's Kinsey Millhone started out at age 32, but the author ages her sleuth two-and-a-half years per book, pledging never to foist a menopausal Kinsey on her readers.
Lee Child's Jack Reacher aged for a while, but the author, sensing rough patches ahead, put on the brakes. Patricia Cornwell has done the same with Kay Scarpetta, and John Sandford with Harry Davenport.
Other mystery masters have chosen to keep the clock ticking for their protagonists. Lawrence Block says that his Matthew Scudder is in his seventies (and has set a recent novel in the 1980s accordingly), and Michael Connelly cops to Harry Bosch being 60. James Lee Burke's Dave Robicheaux is in his seventies (but fit) while Burke's other character, Sheriff Hackberry Holland, is pushing 80.
Bill Pronzini's "Nameless" detective and Marcia Muller's Sharon McCone have grown older, and Walter Mosley's Easy Rawlins has, too. Among other aging detectives are Ian Rankin's John Rebus, Ruth Rendell's Chief Inspector Reginald Wexford, and J.A. Jance's Seattle homicide investigator, J.P. Beaumont. This more realistic approach seems ever-more widespread in the genre, and there are many other examples.
In my Nathan Heller series, I knew I would be moving up through history. So in True Detective (1983), where he deals with Chicago Mayor Cermak and Al Capone, Nate is 27. But in the recent Kennedy Trilogy (Bye Bye, Baby; Target Lancer; and Ask Not), Heller is in his early sixties. And for the first time in these memoirs, the character's death is acknowledged: Nate tells us the JFK material can't be published till after he's gone.
A surprising number of readers have bemoaned Heller's "death" -- though for him to be alive today, he would rival Hercule Poirot's "real" age.
But perhaps that's why so few mystery writers have unequivocally ended the lives of their protagonists. Readers experience something very personal with the best of the fictional detectives, and while practitioners of the craft going all the way back to Conan Doyle may wish to move on, readers often are happy right where they are.
In the line-up that follows are several sleuths whose creators showed them no mercy, as well as several famous detectives who managed to age more or less realistically.