7 out of 10 illegal downloaders are 35 years old or under.
People who download music illegally also spend an average of £77 a year buying it legitimately, a survey has found.
Those who claimed not to use peer-to-peer filesharing sites such as The Pirate Bay spent a yearly average of just £44.
Almost one in 10 of those questioned aged between 16 and 50 said they downloaded music illegally.
However, eight out of 10 of that group also bought CDs, vinyl and as MP3s.
A total of 1008 people in the UK took part in the online poll commissioned by researchers Demos.
Half the group (50%) accessed music officially via YouTube, and 22% listened to internet radio.
Napster, once a pioneer of music filesharing, was used by just 4%, with 21% saying they had not heard of it.
Music streaming service Spotify was used by 9% of the group, most of whom had not signed up for the paid-for premium service.
However, it was rated highly for being easy to use, convenient and providing access to a wide variety of music.
75% of 16-24 year olds said they were prepared to pay for MP3s. The optimum price for the survey group as a whole was 45 pence for an individual track, with just 2% saying they would pay more than £1.
Current chart topper Fight for this Love by Cheryl Cole is priced at 99 pence on iTunes in the UK, and 79 pence on Amazon.
"Politicians and music companies need to recognise that the nature of music consumption has changed and consumers are demanding lower prices and easier access to music," said Demos researcher Peter Bradwell.
It also raises questions about the draft Digital Economy bill, which is due to be submitted to parliament later this month and proposes disconnecting file-sharers who repeatedly break the law.
"The scale of unlawful file-sharing poses a real threat to the long-term sustainability of our creative industries," said a spokesman for the Department for Business, Innovation and Skills.
"While surveys asking people about unlawful behaviour should be treated with caution, it's encouraging that the findings signal that the three-pronged approach set out by the Government this week - a mix of education, enforcement and attractive new commercial deals - provides the best way forward for industry and consumers."