When I was 18 I lived by myself...in my parents house, they were too busy with my stupid brother, who was locked up in Juvenile detention since he was 12...
I did hang out with a lot of bad people but I never did anything that they did...
My parents weren't around but I still had the grey matter between my ears to figure out the difference between acceptable and un-acceptable behaviour.
The 18 year old was probably the peer of the group, the younger ones followed the lead...