A little history. We went through this same issue once before when the drinking age was a variety of ages from 18 to 21 across the states, but the war in Viet Nam brought about the "If I can fight for my country, I should be able to drink" argument that we're seeing again today. By 1972 most states agreed that voting = legal alcohol and lowered the drinking age to 18, which opened the floodgates to accommodate a whole new set of thirsty patrons, and the way to get them in the door was to provide live entertainment.
Clubs sprang up everywhere and live music thrived. If you were a half-decent band, you could easily find somewhere to play almost every night of the week and get paid for it too (none of this "pay-to-play" crap existed).
This was great for the music business because it gave neophyte musicians a place to get it together both musically and performance-wise. Just like The Beatles did in Hamburg in 1962, you could play 5 sets a night 5 nights a week to really get your chops together. Do that for a year or two and you were ready to take the next step towards doing your own thing, if that's what you wanted to do.
Unfortunately, it was also easy to fall into the trap of just playing clubs forever because the money was so good, but those with ambition took their club days for what they were and moved on up. They had learned what they needed to by constantly playing in front of crowds.
This musical support infrastructure is largely gone these days. A band that is considered to be playing a lot today is lucky if they play once a week. That means it will take a group a lot longer to not only get to the point where they're comfortable in front of crowds, but to get musically and vocally tight as well. The longer it takes a band to make progress, the more likely they will break up or change their direction, which means that perhaps the next great trend in music has shriveled on the vine.
Since the drinking age was raised to 21 in 1982, the excitement and diversity in music has steadily decreased. It's bland, it's homogenized, and we've really not seen a new trend that's caught on big since Rap (which hit the mainstream 25 years ago). I attribute this mostly to the large scale closing of the club scene due to the higher drinking age (the tougher DUI laws too). Higher drinking age and more arrests = fewer club patrons. Fewer club patrons = goodbye clubs.
Let's face it - musicians need the constant feedback and attention that only an audience can bring. The more you play live, the better you get at it, which leads to more experimenting, which means the more likely you are to find your own voice.
I hope the drinking age is lowered soon. Music (and the music industry) desperately needs a shot in the arm.
FIVE REASONS TO LOWER THE DRINKING AGE
1. If you can fight and die for your country, you should be able to drink at 18.
2. If you are trusted to vote at 18, you should be able to have a drink at 18.
3. 18 year olds are already drinking anyway. Just go to any college campus and see for yourself.
4. A lower drinking age means more clubs, which means more work for musicians.
5. More work for musicians means better entertainers, better musicians, more interesting music, and ultimately a stronger music industry.