Turning 21 years old is celebrated in many countries as signifying the start of a coming of age and entering adulthood. Various ritual take place around the world to mark this milestone. (See: Colors: the global multicultural magazine)
A British tradition is the giving of a key, which symbolises the person is responsible enough to have his or her own key to the front door, while someone sings the words, "I've got the key of the door, never been 21 before!" It is also considered as being a ceremonial offering of a "key to the future". The key is often signed on the back by well-wishers. (See Te Ara: Birthdays and wedding anniversaries)
Another British birthday tradition is drinking a yard-glass of beer - a tall glass holding 1.4 litres ( 2.5 pints) of ale that is often spiked with a stronger alcoholic drink.