I started to let my characters age with me when I realized that there isn't a "magical" age. When I was a teenager, everything wonderful happened when the character turned 17 or 18. I was a little disappointed that I didn't have a grand adventure like the kids in the books. I think it can be difficult for a teenager to write a convincing adult character. It does boil down to the writer's ability no matter the age, sure, but I've read characters that are supposed to be mature 21 or 22 and both they and their love interest (also earlier 20s) behave like teenagers.
I think age does give you a better insight into creating characters, no matter the age of the characters you create. (My series is a novel. I do understand why a comic artist wouldn't want their OCs to age.) I've read somethings written with a teenage protagonist and often the entire cast feels like teenagers, even the characters that are supposed to be in their twenties. Adult characters are often seen only in familial terms: brother, sister, mom, dad, etc. While adult writers, usually with more experience honing their craft, you can see a more diverse and engaging cast. So even if an adult writes a seven-year-old character, the character usually will feel like a real seven-year-old.