I've been to the first year of Castle of Horrors and definitely thought it was a lot of fun and scary. Castle Of Horrors is geared towardsd an older crowd, but you will probably see quite a few high school kids. But most will be college age and older. I'm in my late 30's and go with my fiance to most of the Rochester Haunted attractions each year and have never had an issue with the younger crowd. I'll be going to Castle of Horrors again. The high school kids always tend to look far more scared in the line waiting than the over 21 crowd...LOL!
For the biggest indoor attraction, Nightmare Manor definitely is the place. I go to this one every year and love it too.
Nightmare Manor
Nightmare Manor will probably have more high school kids than COH though.