I turn 27 on Friday (yes, Friday 13th - I was actually born on a Saturday, though, which I think makes me the devil's nephew rather than his son ;) ), and as a huge fan of The Doors and Nirvana, I can't help thinking that that's the age at which people 'die young'.
As a teenager, I was obsessed by the glamour of that idea - perhaps unsurprisingly, I was the moody, insular kind of teenager, the kind who get branded 'emo' now (a label I'm fortunately just too old for). I discovered Nirvana when I was about thirteen and wallowed for a long time in Kurt Cobain's rather sad life story. I guess puberty makes everyone feel a little self-destructive.
Anyway, I became sure that I would die young - that I would have a brilliant career, be a millionaire by 25, and then die at 27 of some non-specific consequence thereof (as well as being gloomy and melodramatic, it should be acknowledged at this point that I was also insufferably arrogant - I may still be, but hindsight makes it painfully obvious even to me >_>).
The bad news is that I haven't had a brilliant career yet. The good news is that I've managed to grow out of my desire to die young. This is mostly to do with not having pubescent hormones playing havok with my better judgement, but there's also probably an element of real growing-up involved.
There's also the realisation that lots of people die at other ages than 27, of course. Leonard Cohen is my favourite living songwriter at 79, despite definitely doing a fair amount of living fast when he was young. Keats, my greatest literary hero, died at 25 (which isn't really much comfort, since it means that by the time he was my age, he'd already written almost everything on my 'top 10 favourite poems' list).
At first glance, the names and obituaries look compelling. It's certainly true that some of the most-canonised icons of the 20th century died at 27 - besides Cobain and Jim Morrison, the most famous are probably Jimi Hendrix, Janis Joplin and Brian Jones of the Rolling Stones - but then, others escaped. Keith Moon, for example, made it all the way to 32. Despite his best efforts, Keith Richards is still going (hm... maybe it's something to do with being called 'Keith'?). James Dean went early, at 24, though if you'd asked me before I checked for this article I'd have sworn he died at 27.
Wikipedia cites a study claiming to show that there is actually no cluster of deaths among the young and famous at 27 (though musicians are apparently more likely to die young, just not necessarily at 27), but there's definitely a cluster of remarked-upon deaths at 27. That makes this a media phenomenon, and they can start for any reason or none at all. The cluster of deaths from 1969-71 (Jones, Hendrix, Joplin and Morrison) certainly make for fertile fodder, and apparently a remark of Cobain's mother at the time of his death may have contributed to the myth taking root.
There's an interesting and serious question about how dangerous the myth is - on the one hand, there was a time when I wanted to die young, and I can't be that unusual in that regard given how much fuss was made over the more recent death of Amy Winehouse, but on the other it's hard to claim that most people don't grow out of it long before they hit 27 themselves.
The question that more interests me (though it's arguably a less important one) is this. Most media myths take root because they fulfil some cultural-psychological need. A simple example is 'the immigrants are taking all the jobs' - it explains why there are no jobs without having to acknowledge the real reason, that the economy just doesn't have that kind of jobs in it anymore. What, then, is the social function (for want of a better expression) of the myth of dying young? I really don't have an answer, despite having experienced its power very strongly myself for quite a long time.