Higurashi is also lengthy.
Here are some suggestions on my end, I'll try to make only appropriate ones content wise but I haven't seen any of these for a long, long time.
Amatsuki
Black Blood Brothers
Ayakashi (not the old school one) : This one is battle heavy but I don't remember it bein' that violent.
Asu no Yoichi! : Has a decent amount of fan service, nothin' to bizzare for a teenager though. It's also really funny and has a decent message.
Rideback: Very, very good anime about fightin' against corrupt politics but may be to serious. It's not violent but it's also not funny or anything at all, ever.
Viper's Creed: Pretty much like the above but battle heavy. It's mostly mech type fightin' though. I don't remember it bein' gory at all and I figure if a teenager can grasp the story they'd find it very enjoyable.
Sengoku Basara: Very teen appropriate. Has a lot of good in it but due to the period it may teach kiddos that fightin' is actually a good thing.
These are all 12-14 episodes long. You'd also have to stream them though, except for Black Blood Brothers which has been licensed here and complete. I'm not sure if parents of pre-teens would enjoy their kids watchin' these though, but I'd show them all to my Nephew if he was in that age range. You just never know these days. Then again, due to the circumstances, they may not have parents for all I know and have been through far worse already in which they could stand to learn a few things from all of these.