1986 when I joined ...old enough to fight, old enough to drink. 17 and bar crawling...
1987... 19 to drink if military, I got assigned to Korea...old enough to see over the bar, old enough to drink...18/19 bar crawling in a foreign country including a 4 day pass + 48 hour pass when I reupped...6 day thunder run from Itaewon to Bong Il Chon
1989...21 to drink if military... Went back to Campbell and hung out at a bar where they knew me from before... showed them my ID on my 21st birthday and we all laughed about it
21 1/2 - charged with DUI (didn't stick, dismissed from court)
My point is that there isn't enough behavioral difference between 17/18 and 21 to make it matter what the drinking age is. Soldiers will always drink, they will always get in fights and they will always do stupid shit. It's about individual responsibility and maturity, not age. The biggest difference is that if you lower the drinking age, the younger soldiers will lose some of the mystique around it because it's no longer doing something that is forbidden. They won't have to hide what they are doing any longer.
<Begin rant>
This is all more PC bullshit. The warrior class is a different breed. Work hard, play hard has always been the motto for those that voluntarily put themselves in harm's way. The closer to the enemy the harder the play. Work hard, don't play is a recipe for disaster. If you have the major stressor of military service, which is only worsened by deployment and combat deployment, you have to have some release. It's different for everyone. If you make all of the forms of release verboten, then you end up with strung out, stressed killers with no productive way to burn it off. For me relieving stress was getting out of the barracks, hanging out in a bar with friends, having a few (or more than a few drinks) and getting stupid while trying to get lucky with some of the local ladies. The next day I'd feel like hell, but I was good for a long time after. There's just not a good way for the military to replace that form of release. I'd have probably lost it along the way if I hadn't been able to burn stress that way. I always knew no matter what kind of crap was going on or how bad the suck was that there was a good time with friends waiting at the end of it. So yes, I say lower the drinking age. A lot of really good troops that are exactly the kind of people we need are getting drummed out of the service or having their careers ruined for alcohol related incidents, and non-alcohol related incidents that come from being bored, that shouldn't even be an issue. It used to be that no one made E6 without at least one Article 15 resulting in loss of a stripe. Now an Article 15 ends a career and more than a few of them are directly related to the drinking age.
Yes, the services need the soldiers that play by the rules but they also need the steely eyed killer that parties hard when not engaging the enemy.
<end rant>