I think we've been through this before. Angry people get more angry when they drink. Age is not a factor. The people that I drink with have never been habitually angry and we are all just fine when we drink.
If you find yourself drinking with angry people I recommend you find new drinking buddies, nice people that don't start bar fights.
Although your answer is right, I think it misses key points.
Younger drinkers drink socially, and a high percentage of 20's and 30's people frequently go out to do so. They are happy to be going out with friends, the bar scene is new, and they tend to be happier going in to the evening. (plus, they are out and about rather then at home hitting f5 on message board).
Then, you get to the older 40's, 50's and 60's drinkers. their contemporaries have careers and families and spend time with them rather than bar hopping all week. Less of them out there.
Many of the ones that are, are doing so to escape job/family pressure... going in to it with a sketchy mood.
Then, you have the home drinkers. for whatever reason, they need to numb their minds frequently and in solitude... not a very healthy endeavor, and one that is not usually embarked upon with a happy go lucky mindset.
You are completely right that Happy people are happy drunks, angry people are angry drunks... but I would bet the angry and unhappy older people tend to continue drinking with greater frequency than happy people as they age.
I was always a happy drinker, used to go out a couple times a week at least. now, after I hit the big four-oh, I think I have had about 5 beers in the last 2 years.