I wouldn't consider mid 60s to be young by any stretch. You make it into your 50s, then you've lived a pretty decent life. But yeah, the death toll is pretty high in the music world. 

Dimebag Darrel of Pantera fame was murdered at 39.

Metallica bassist Cliff Burton was killed in a bus crash at 24.

Jeff Hanneman, co-founder of Slayer, died of liver failure at 49. 

Megadeth drummer Gar Samuelson died of drug overdose in his 20s.

Drowning Pool singer Dave Williams died of a heart condition in his 30s

Peter Steele, frontman of Type O Negative passed away from an aortic aneurysm at 49.

Mitch Lucker, frontman of Suicide Silence was killed in a motorcycle crash at 28.

Avenged Sevenfold drummer Jimmy Sullivan, Wayne Static, singer for Static X and Paul Grey, bass player for Slipknot, all died from drug overdoses in their late 20s and 30s.

Randy Rhodes died in a plane crash at 24. 

And most recently, both Chester Bennington of Linkin Park and Chris Cornel of Sound Garden both committed suicide.

I think a big part is the culture of it all. Touring, performance and making music are all difficult and stressful endeavors. Many musicians seek refuge in drugs and alcohol, partying inhumanly hard to forget their problems. Even when they do sober up and get clean, the damage to their bodies is already done, and they pay the price down the road. 

Another contributing factor is the emotional toll, baring your soul to the world for so long, relieving your life's hardships night in and night out, both on and off stage, combined with drugs and booze, pushes even the strongest of men over the edge. 

Other times, it's just fate. Tragically passing due to circumstances outside of their control. And we only notice cause they are our heroes. 

There was a piece on the BBC website last year that looked into why celebrities generally seem to be dying, and it boiled down to:

There are a few reasons, Nick Serpell says.

"People who started becoming famous in the 1960s are now entering their 70s and are starting to die," he says.

"There are also more famous people than there used to be," he says. "In my father or grandfather's generation, the only famous people really were from cinema - there was no television.

"Then, if anybody wasn't on TV, they weren't famous."

Many of those now dying belonged to the so-called baby-boom generation, born between 1946 and 1964, that saw a huge growth in population. In the US for example, the census bureau said that 76m people in 2014 belonged to the baby boomer generation - some 23% of the population.

I will also observe that men in particular, but women too,  have a spike in mortality rates in their late teens and early 20s - when a lot of people get a lot of freedom but haven't yet developed a more adult mindset. So there will be a few musicians in that category that will die and generate headlines exactly because they are young (as an interesting aside, if you make it past that point then your life expectancy climbs quite a bit*.)

There is also a myth that musicians seem to die at 27, which I understand to be false.

*obviously, given that the life expectancy of a 35 year old is always going to be 35+, but it's a rather more risky period of your life that if survived means that you're much more likely to get to your 50s, which is where I think the next particularly dangerous age range is.