We in the Western world are used to names being fixed since our birth. In other cultures it is different. Indians, for example, used to take new names after significant events. Chinese children were sometimes given permanent names only at the age of three, when a monk would visit their house and choose a name for the child.
Nowadays, most urban Chinese have English names. They select these names for themselves in English lessons at school. Then they use those English names when talking to Westerners.
The modern Westerner has a name he chooses for himself, too. It’s the Web name. If one acquires even a little Web fame via one’s blog or some social site, the username becomes a name for all practical purposes. Sometimes, people are even called by their Web names in real life. (This hasn’t happened to me yet, though.)
My seven-year-old son already has a Web name he has invented for himself, and I’ve heard a friend call him by that name. Now that’s a child of the 21st century!