Time in comic books doesn't work the same way it does in real life. Characters rarely show any signs of aging and usually remain the same age throughout all their stories. Would we want to seem them age? Some characters have aged a bit since their first appearance. Does this keep the character from getting stale or are we running the risk of having our characters get too old for future generations?
== TEASER ==
I've mentioned before how I started reading/collecting comics in 1984. Back then, Spider-Man was in his mid-20s (he still is, I guess). Now if he had aged normally from then, he'd be close to 50. Obviously that would limit future stories with Spidey. On the other hand, it's not like he's frozen in time. When he first appeared in 1962, he was still in high school. We have seen him graduate and even go through college. Perhaps Spider-Man aged too much. We saw him get married and even have a kid (well, he didn't have it, Mary Jane did). Apparently this made it hard for readers to relate to him? Weird since I'm married and have a kid.
We have seen other characters show signs of aging. Dick Grayson started out as a kid and now he's in his mid-20s. There is no fixed rate at how time passes in comics. There's no formula saying one issue equals one day for characters. I believe in Green Arrow #1 it was mentioned that something like six months had passed since Star City was destroyed and brought back when it hasn't even been six months in 'our' time.
If characters start showing signs of aging, that limits their longevity. Batman has been around for over 70 years. While it's good for character development to see him and others age, don't we want to be able to enjoy them for as long as we can? Don't we want our children to be able to enjoy them as well? We've seen an "older" Bruce in The Dark Knight Returns as well as Batman Beyond but it's not the same. Where should the line be drawn? How much should writers and publishers allow characters to age? You can't just age some characters, you have to age the entire comic universe. Should growing older be one battle that superheroes can win?