What is the age limit for drinking alcohol?

The legal drinking age is now 21 in all states. A few years ago the drinking age varied by State.

But, <sarcasm on> in keeping with the spirit of the tenth amendment to the U.S. Constitution stating that all authorities not specifically given to the Federal Government by the Constitution belong exclusively to the States; the Congress passed a law forcing the States to make 21 the legal drinking age, and the Supreme Court, the defender of the Constitution, declared this direct affront to the Constitution legal.

The age does vary however in differing countries i.e.18 years old to enter bar and consume in the UK.