For these purposes, adult is 17 or older, old enough by the ESRB to buy Mature rated games.
Please keep games to Mature rated or lower (no AO games).
For me, it was the intro scene in Dead Rising with the mother and the daughter and it implied that they got eaten by the zombies. It shook me up - BAD - when I was 15 or so and first saw it. I am 21 now and that scene literally gives me the chills. Funny thing is that Dead Rising itself, the game and the cutscenes within the game don't bother me. I love Dead Rising, but a fair warning - if you start it, you go into the game. Don't go get a popcorn or a drink, start the game, load your game, and pause when you're in the mall. If you leave it on the intro screen for over 30 seconds, you get this: https://www.youtube.com/watch?v=-BNjgDn5Dkk. You get to see the character personalities and their last five minutes of life. I can't watch the whole thing. DR came out in 2006, so I'd imagine that scene upset a lot of people born in the 1980s if not even earlier.