I voted Yes, but just to play the devil's advocate:

What about the fact that most kids turn 18 while they are still in high school? Wouldn't this mean that it would be MUCH easier for high schoolers to have access to alcohol?

Knee-jerk response = they have access to it anyway from older siblings, friends, cousins, etc. But I would argue that this source is limited. When I was in high school most people just didn't have a source to get alcohol from on a regular basis. Many 21+ siblings are off at college or busy working or in the military, where they can't pick up for their siblings.