Tabitha

While it's true that shoujo, shounen, seinen and josei are all only target demographics, they generally do really indicate to which gender the series might be more enjoyable to, and what kind of style might be used. Most of the time I can tell by the first glance whether a series is shounen, shoujo etc.

Exceptions exist. Some 'shoujo' stories made by female mangakas get published in shounen magazines, and vice versa in shoujo magazines, deliberately put there in hopes of gaining a wider audience.

There are action stories made by female mangakas - with lots of bishounen characters.

There are stories of girls having tea parties and doing just normal daily things and nothing, by male mangakas. Might a girl read a series like this? She might. But to whom does this in general appeal to? Male audience.

There are lots and lots of shounen and seinen series I love, admire, and truly enjoy - as much as the opposite holds true. I can't stand supposedly 'cute' girls doing just 'cute' things. Or a series about a pathethic nerd boy to whom suddenly all the world's hottest, cutest and prettiest girls and women gather around. I'd rather read series without too much fanservice for men, as it's usually disturbing, and offputting for me.

I like too many shounen and seinen series to list them all (hundreds, a thousand or so), but here's a few:

Vagabond, Naruto, Blade of the Immortal, One Piece, Dragon Ball, Hikaru no Go, Death Note; all the basic stuff which seems to gather a large audience across the gender bounds.

I must sound mad, but nowadays, every now and then I see and hear comments: 'this could be shoujo as well as seinen' and 'it's not a genre, so it doesn't matter', 'it doesn't mean anything, why wouldn't girls like it?' etc. I think that shounen, shoujo, seinen and josei all mean something. Most often they are good indicators, as to what the series might offer you.

If I had two choices (without seeing a further description, or the art style):

1. shoujo story with romance

2. shounen story with romance

I would blindly choose 1. My brother would choose 2.

Now I fear I might have lost the point I wanted to make, somewhere along the lines. However, I'll say this: think about the audience. Think when you suggest series, to beginners and old consumers alike. Think before you go exclaiming "this can't be shoujo/shounen!" - first see whether the artist/author is female or male, what style is it drawn in, what is the storyline, is there any fanservice (and for which gender), what has the mangaka generally made - more shounen or more shoujo series?

Maybe one day there will come a time when we don't need the target demographics anymore, and all series attract all genders/genderless people and everything in between. Well, until that time, those tags are there for a reason. Most of the time!