Easy to understand consequences. For instance, my 17 year old once let his friend drive our car. He lost driving privileges for a week. Did not happen again.

Easy to understand consequences. For instance, my 17 year old once let his friend drive our car. He lost driving privileges for a week. Did not happen again. For excessive computer use, the 18 year old looses access to home-cooked meals, driving the car, money, laundry, etc. You could also tie it directly to the computer, such as limiting wifi or phone connectivity if usage goes above a certain level.