To sum up "what would happen," because it involves an age restriction all of the hysteria associated with drunken driving and the Neo-Prohibitionist groups (MADD, SADD, etc.) will be brought down on you. You will not be treated fairly. Normal due process and rules of evidence will be halfassed, you will be presumed guilty from the beginning, and even your own lawyer will treat you like a stupid kid with no self-control. A loser.
Every society has it's bad habits and ours is closing the barn door after the horse is gone. All the dumb-show and oppressive, inflexible enforcement won't bring back the dead kids, but at least the politicians can show that "they care" and put the target on someone else's ass. The grotesque example is the security theater at airports, but more pervasive examples are the weapons policies at schools where kids get in trouble for drawing pictures of guns, and youth vice regulations where they think the world will stop spinning on its axis if a 19-year old drinks a beer. Note they always target people who aren't in a strong position to fight back.