@Gravewind Seinen is also for teenagers... older teens... but still... it's pretty research friendly... so it's not unusual it's in a seinen magazine...
@Krisawo It's not just because of the magazine. Lots of things in Deathnote kinda flew over the heads of the kids reading it... but they thought it was cool... so it worked....
Of course, when something is targeted towards older teens, it can be either shonen or seinen... teens don't seem to get their own section... it's either children to teen or teen to adult.