Yes, it is time. Lowering the drinking age would make 21 years olds behave like 21 years olds, and not like 16 or 18 years olds. It is astonishing how much effect the drinking age has on maturity.
I certainly don't want to call my fellow Americans particularly mature, but it's pretty rare for people to wait until 21 to drink here, so I think the effect is dispersed.
More recently, they've started to crack down on underage drinking, and now the police blotter fills a column in the campus newspaper with a series of "Driver arrested on suspicion of DWI." Hopefully this is a result of them cracking down on drinking and driving too, but I fear that to some extent it's because they are forcing the parties off campus.