I haven't noticed it in my reading, but I'm probably just not well-read enough. But I'm pretty sure the (longform story, fantasy genre) webcomic script I wrote at 17 was humorless, or nearly humorless. I was even aware of this at the time, but didn't try very hard to do anything about it. I think I had trouble mixing humor and non-humor at that age.

I'm trying to think back on whether other writers my own age had the same problem, but I can't remember, except that stories we wrote together (usually by taking turns writing a paragraph or three at a time in a chatroom) usually did mix humor with serious-tone fantasy. This makes me wonder if being used to writing for an audience has something to do with it. The immediate feedback of working together that way made me feel a lot of incentive to write things that were entertaining.