We’ve probably done this in the past. Maybe more than once. But I don’t recall it, so here it is.
Some movies, book series, and comic strips actually show characters aging. We’ve been witness to Indiana Jones aging of late. But it’s much more common to see characters remaining the same age through time. Especially comic book and comic strip characters, and especially kids. (In a story in Mad, they showed the character Henry continuing to act like a kid. when someone asks him how he stays the same age, he replies that he’s a bald diminutive person, and he’s been 80 years old all along. Of course, that just makes you wonder how he could be 80 all those years.)
Superman, Batman, and Wonder Woman have been around since the 1940s or earlier, (So has Prince Namor, the Sub-Mariner). Marvel’s original stable of superheroes has been around since the 1960s.
Some notable examples:
Sherlock Holmes and Dr. Watson – they remained pretty much ageless throughout the run, although Doyle did give us Holmes and Watson in retirement in His Last Bow. It remained for pastiche writers to give us truly old (or young) versions.
Nero Wolfe and Archie Goodwin – Rex Stout kept them in their 50s and 30s, respectively, throughout a nearly 40 year run. No explanations given. Robert Goldsborough kept the ages when moving them into the 1980s and 1990s, then relapsed into the 1930s.
Tarzan – He pretty much stayed the same through most of his 30+ year run. He fought the Germans in WWI and came back to do it in WWII. Then the movies kept him going into the 1970s, at least. There were two attempts to explain his apparently perpetual youth using magic from as couple of his adventures.
James Bond – Fleming only wrote his adventures over a 15 year span, so he wasn’t long-lived during the life of is creator. Except, of course, that Fleming portrayed him as a spendthrift because he expected to be killed at any time during the course of his work. Bond lived long for a character of his type. But then his age was greatly extended by the movie series and by continuation of his literary adventures by a succession of authors. Some of them kept him a period character, but others tried to update him to be contemporary. Bond outlasted the Cold War milieu that created him and, lately, the racism, sexism, and nationalism that defined him. The latest reprint of his books tried to bowdlerize that, and still had a reader’s warning at the front. Contributors to the franchise never tried to account for ow a WWII agent was still operating as a young man after the turn of the 21st century
Frankenstein and Dracula – well, you know, they’re monsters. They’re effectively immortal. The Mummy’s been aroiund for thousands of years. And when grave robbers opened the tomb of Lawrence Talbot during a full moon, they found that the Wolfman, at least, was just as immortal.