I was going to split the difference and guess that he was older than Katou but younger than Iwaki. However, Lore thinks that Nitta-sensei tends to draw the men as hot and young-looking, and the use of "kun" probably indicates that Yoshizumi is slightly older than Iwaki (see the comments of the original post for details). l agree that seems likely, especially when I think about the time that Iwaki goes to visit Yoshizumi after the argument with Asano, and Yoshizumi pats him on the head in a big-brotherly manner, saying, "You're a good boy, Iwaki-kun." (Part 2 of "Jamais Vu," Book 10)

Unfortunately, that kind of messes up my fanfic plot where Yoshizumi, Onozuka, Miyasaka, and Asano are all auditioning for the part of Kikuchi's lover, a man in his early twenties. I guess I can add a comment that Yoshizumi looks much younger than he really is. After all, Asano is recast as Aizawa after Yoshizumi is injured, and I get the impression (though I could be wrong, of course) that Asano is in his twenties, so the age difference doesn't seem to be a problem in the director's mind. Although Aizawa's age doesn't really seem that crucial to the story, anyway.

On the other hand, Mochimune also addresses Iwaki as "kun," and he appears to be younger than Iwaki. In "Core Curriculum" in Book 11, Iwaki thinks to himself that Mochimune is "younger than I thought...I heard he was about my age." If he was expecting someone his own age, that implies that Mochimune is younger than him, maybe in his late twenties? On the other hand yet again, Mochimune obviously doesn't care that much about politeness, and he could be using "kun" as a deliberate means to provoke Iwaki. But on the third hand ^_^, even after they come to a mutual understanding and respect for each other, and Mochimune actually apologizes to Iwaki for his rudeness in "Couple Awards" (Book 13), he still calls Iwaki "kun". (And also still manages to throw in a subtle insult when he says that he assumed Iwaki was the supporting actor in Fuyu no Semi.)

So maybe it's just Mochimune's innate arrogance that he addresses anyone "beneath" him as "kun"--a director, I assume, would normally rank above the actors as he is sort of their boss, although I admit that I'm only guessing, based on TV dramas that I've watched. I suppose it also depends on the relative statuses of the specific director and actor in question. I had my OC director Kitamura address Kikuchi as "san" out of respect for Kikuchi's veteran status, considering that Kitamura is younger and fairly new to the business. And I have been wondering if Mochimune would have the balls to address Kikuchi as "kun" if they worked together. What am I saying? Of course he'd be capable of it! I think he'd be capable of almost anything short of murder in pursuit of his artistic vision. The question is whether provoking Kikuchi in that manner would be of any benefit to Mochimune as a director. He did similarly provoke Iwaki by challenging his pride as an actor when he was trying to recruit Iwaki for his movie. The collision of those two massive egos (referring to Kikuchi and Mochimune, of course) would certainly be fun to watch!

I do agree with Lore's reply to my comment to the original post that it's difficult to tell the characters' ages by looking at them. I'm not sure that I would have guessed that Iwaki was older than Katou if we hadn't been explicitly told so in the manga. His face is pretty youthful; it's more his serious demeanor--compared to Katou's youthful impulsiveness--that conveys an air of maturity to me. Aside from the obviously "old" characters like Iwaki's dad, the only characters whom I immediately assumed were over the age of thirty were Kikuchi and Iwaki's brother Masahiko.

And with Kikuchi, it's partly due to references in the story that make me assume he's older. If I were just looking at the drawings, I think I would guess early-to-mid thirties. But it's implied that he was already a star at his peak when the scandal broke ten years ago, with many films under his belt: "I've seen all your movies," Iwaki tells him. If Kikuchi had only made one or two, Iwaki would've said something like, "I saw your movie" or "I saw both of your movies" (unless he's also seen Kikuchi's American films). But it's mostly Iwaki's fanboyish excitement upon meeting Kikuchi that makes me think Kikuchi must be older--he acts like a kid meeting his hero. So with that in mind, I'm bumping Kikuchi's age up to late thirties or early forties. (In my mind, when I'm writing my Kikuchi/Onozuka stories, Kikuchi is 40, and Onozuka is about 24.)

Masahiko also doesn't really look that old, but his very stern demeanor and stick-up-his-butt attitude definitely give the impression that he's older than Iwaki. In "The Plunderer" (Book 9), when Katou is looking at Iwaki's baby pictures, he finds a photo of young Masahiko holding baby Iwaki, and Masahiko looks to me like he's in his early teens, maybe middle school age, which means that he's older than I thought, at least in his mid-forties when I would have guessed late thirties otherwise.

I would guess that Shimizu's in her thirties; Kaneko strikes me as being younger, both in his age and demeanor--he seems a little inexperienced and out of his depth at times, but to be fair, Katou is a very challenging client. Onozuka and Miyasaka seem to be in their early twenties, although Onozuka is cynical and conniving beyond his years.

I'd love to hear any thoughts or comments that you guys have! And if anyone's more familiar with Japanese honorifics, please feel free to correct me if I'm totally off-base with the "kun" thing.