The average age for US kids to first acquire digital content is 7

"Forty-one percent of kids who own some form of digital content said music was the first type of content they downloaded, with 38 percent saying it was game downloads. The average age at which kids make their first digital acquisition is 7 years old. Girls in particular turn to single song downloads when they first foray into music, and their predisposition for music also makes them slightly more likely than boys to first get ringtones.
"Forty-three percent of digital downloaders were six years old or younger when they acquired their first digital content," said Anita Frazier, industry analyst, The NPD Group. "Since parents are the first touch point for children this age, it is important for companies to develop marketing strategies that reach parents as well as kids.""
Source: Press release from NPD, 5th January 2010