In 2006, a teenager started a live music club night, open to his underage peers. As a 14-year-old music fan who had been brought up on his father's record collection, Sam Kilcoyne was fed up with the lack of musical entertainment for himself and his friends.
Fans swarmed to his night at the Coronet, in London, and the following year he launched the Underage festival, for attendees aged 14 to 18.
Kilcoyne kept one mission in mind: to book only decent acts. Soon the one-day festival grew from 5,000 people and 40 bands to become an essential annual event for 10,000 festival goers and twice as many acts.
This month, the event celebrates its fifth year and throws its net further, to 13-year-olds.
For many of those attending, it will be their first experience of a music festival. Last year, Underage achieved a coup by booking M.I.A as its headliner, and this year's line-up, influenced by teenagers using the festival's Facebook page, is one of the best for rising talent, with indie-rock from The Last Shadow Puppets' Miles Kane, Pulled Apart By Horses and Bombay Bicycle Club and hip-hop and rap from Roll Deep and Maverick Sabre.
With acts such as Janelle Monae, whose disco-soul has been championed by Outkast's Big Boi and P Diddy, Underage also proves that its line-up does not have to be safe and unchallenging - a criticism which has met some much larger festivals as they have struggled to shift tickets this year.
Kilcoyne may have long left his role as the festival's founder and organiser to concentrate on playing keyboards in the hardcore electro band S.C.U.M, but he can be proud that he helped to pave the way for more teenagers to attend music events than ever before.
More promoters are lowering gig age limits to 14. Tom Baker, a promoter at Eat Your Own Ears, which has taken over Underage, says: "Sam probably started something. Underage started because a lot of gigs were for over-18s. I try to make all my shows 14-plus, and more and more promoters are trying to encourage younger people to come. More want to see venues open up the doors a bit - after all, they know that 10,000 teenagers are going to an event every year."
Kilcoyne is not the only teenager who has felt that his age group should be recognised.
There are now websites dedicated to the cause, run by teenagers, such as Teen Today, a hub for teens with a detailed calendar of teen-friendly gigs.
The first UK-wide underage gig listings guide, UnderageGigs.com, was formed in 2009 after its founder, Piers Marais, found that there was no simple way to find gig tickets as a present for his 15-year-old sister.
As a band member himself, playing underage gigs around the country, he decided to gather all the relevant information on one website. When Marais started the site in 2009, he had around 300 events listed at any one time. Now that figure is around 2,000.
While pop has always catered to a teen market, with the likes of the Spice Girls, JLS and Girls Aloud opening their doors to teens, it has taken a while for indie-rock to catch up.
The 2007 boom in teenage indie bands - including Cajun Dance Party, Bombay Bicycle Club and Pull In Emergency - arrived in tandem with Underage Festival, fuelling a burgeoning teen music scene. The result was more indie-rock gigs and music events for younger music fans.
Later this month, BBC Radio 1Xtra will host its first underage club night, The 1Xtra Club, which will see teenagers flock to the IndigO2 to hear DJ sets from Loick Essien, Sneakbo and the 1Xtra DJs MistaJam, Tim Westwood and DJ Target.
This Friday, Underage Festival celebrates its fifth year at London's Victoria Park. It was the first big music event for teenagers, run by teenagers, but it's unlikely to be the last.