It was smart to use the word "need" in the past tense, since 18 year olds have largely stopped voting since the draft was ended.
As for drinking laws, what argument can be used to establish that 21 is the magical age at which people exercise "good judgment"? I'm aware of scientific findings that the "judgment center" of the brain is the last to develop. But if we go by that criterion then the age of consent for everything from contracts to sex to alcohol use should be raised to about 25, since that is the current consensus as to when they average person has a fully matured brain.
18 was a very common drinking age until recent years when the Feds withheld funds from states that refused to raise it to 21. It's interesting that conservatives who favor states' rights were often the most vocal supporters of raising the drinking age by imposing the will of the feds on the states. They also do this with their attempts to ban gay marriage nationally, enforce uniform drug laws, impose the will of the DEA over states that legalize medical marijuana, etc.
The Clinton administration behaved in a more classic manner, favoring federal authority over states' rights when Janet Reno's office went after the west coast medical marijuana laws. And once again, we see that "left" vs. "right" is an inadequate description of the spectrum of political views, as one would have expected a more liberal administration to be in favor of greater freedom. Quite the contrary, under Clinton many freedoms were curtailed, a tradition enthusiastically embraced by our current president.

