:::: Slow down, slow down... The MIT folks aren't wrong  they're stating an opinion and a judgment that you disagree with. But the real point isn't MIT  it's the age ratings. The Wiki entry for seinen defines it by age  see the quote above, or the entry itself. Brenner's book (see above) also defines "seinen" partly by age. The word itself means "adult age; majority" (as in no longer being a minor), and that's from Breen's EJDic. Roughly, it means "young adult." That is age-graded, and corresponds to many aspects of Japanese culture in which age is significant socially and culturally. 

 :::: In US marketing, manga is age-rated. Since I am discussing US marketing, seinen corresponds to "OT" = "older teen" or to "M" = "mature" (meaning over 18). The reason for this system in the US is concern by publishers and public about sexual content. The US publisher Eros Comix used 成年 as part of their logo for their Mangerotica line (the kanji mean seinen). In that context, the term means "sexually explicit." In other contexts, it means other things, but they all refer to reading material suitable to a young adult, not a young teenager. These definitions of "seinen" aren't up for grabs  they've become quite standard in the US (as Brenner's book shows). These usages simply do not reflect or represent the demographic of the original Japanese publication. Maybe they should, but they don't. 

 :::: This gets me back to Nihonjoe's misunderstanding of what I said above, where I inserted a comment. For US publishers, cross-over readership is very important, because in US marketing, manga are not generally gender-coded. The major exception is the use by Viz  which is owned by Shueisha and Shogakukan  of the terms shojo and shonen for some of their manga (and of of course the Viz Shojo Beat magazine  no macrons in these, BTW). The current issue of ICv2 has some comments about this; cross-over readership is not trivial in the US. 

 :::: In turn that leads back to Azumanga Daioh. By US marketing standards, if AzuDai really is seinen, that means it very likely has sex in it, and explicit sex into the bargain (like Eros Comix paperback book Hot Tails, by Toshiki Yui, which has the seinen kanji on the cover, and is seriously X-rated material). But AzuDai doesn't have any sex in it at all. Instead, it's about relationships among the girls, their lives and friendships, hopes and futures. Yes, it is quite shōjo manga-esque. But seinen it is not, not in US marketing terms. Instead, as the ADV rating for the manga and the DVD put it clearly, AzuDai is "T 13+". 

 :::: So if you want, by all means include the original Japanese demographic, if you have reliable sources for it. But I agree with Peregrine Fisher  a lot more information is needed by a US audience about such things. Personally, I'd like to see the US publisher's age rating included in the infobox, because that's where the stuff is being sold  right here in the US. Calling AzuDai seinen suggests that it's porn or soft porn, which is seriously amiss. (The same holds for Rozen Maiden.) In fact, I think the US publisher's age rating would be much more valuable than the Japanese demographic, which I suspect interests only serious otaku but few other people. 

 ::::